Method for detecting foreign material, and apparatus and system therefor

ABSTRACT

A power transmission method for a wireless power transmitter, the power transmission method including receiving, from a wireless power receiver, a packet including a foreign object detection (FOD) status packet; determining whether a foreign object is present in a charging area of the wireless power transmitter based on the FOD status packet; and generating a foreign object detection indicator indicating whether the foreign object is present in the charging area of the wireless power transmitter based on a result of the determination and transmitting the generated foreign object detection indicator to the wireless power receiver, wherein the FOD status packet includes information on a reference quality factor or a reference peak frequency, and wherein the packet further includes at least one of a signal strength packet, an end power transfer packet, a power control hold-off packet, a configuration packet, an identification packet for transmitting receiver identification information, an extension identification packet, a general request packet, a special request packet, a control error packet, a renegotiation packet, a 24-bit reception power packet, an eight-bit reception power packet, and a charging status packet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.18/181,208 filed on Mar. 9, 2023, which is a Continuation of U.S. patentapplication Ser. No. 17/183,012 filed on Feb. 23, 2021 (now U.S. Pat.No. 11,652,371 issued on May 16, 2023), which is a Continuation of U.S.patent application Ser. No. 16/327,622 filed on Feb. 22, 2019 (now U.S.Pat. No. 11,005,303 issued on May 11, 2021), which is the National Phaseof PCT International Application No. PCT/KR2017/009208 filed on Aug. 23,2017, which claims the priority benefit under 35 U.S.C. § 119(a) toKorean Patent Application Nos. 10-2016-0117518 filed in the Republic ofKorea on Sep. 12, 2016 and 10-2016-0106789 filed in the Republic ofKorea on Aug. 23, 2016, all of which are hereby expressly incorporatedby reference into the present application.

BACKGROUND Technical Field

Embodiments relate to wireless power transmission technology and, moreparticularly, a method of detecting a foreign object placed in acharging area of a wireless power transmitter, and an apparatus andsystem therefor.

Discussion of the Related Art

Recently, as information and communication technology has been rapidlydeveloped, a ubiquitous society based on information and communicationtechnology is being developed.

In order to connect information communication devices anytime anywhere,sensors equipped with a computer chip having a communication functionshould be installed in all social facilities. Accordingly, supplyingpower to such devices or sensors is a new challenge. In addition, as thetypes of mobile devices such as music players such as Bluetooth handsetsor iPods as well as mobile phones have rapidly increased, it isnecessary for users to take more time and efforts to charge batteries.As a method of solving such problems, wireless power transfer technologyhas recently attracted attention.

Wireless power transmission or wireless energy transfer refers totechnology for wirelessly transmitting electric energy from atransmitter to a receiver using the magnetic induction principle. In1800s, electric motors or transformers using the electromagneticinduction principle have begun to be used and, thereafter, attempts havebeen made to radiate electromagnetic waves such as high frequencies,microwaves and lasers to transfer electric energy. Frequently usedelectric toothbrushes or some wireless shavers are charged using theelectromagnetic induction principle.

Up to now, a wireless energy transfer method may be roughly divided intoa magnetic induction method, an electromagnetic resonance method and aradio frequency (RF) transmission method of a short-wavelength radiofrequency.

The magnetic induction method uses a phenomenon that, when two coils arelocated adjacent to each other and then current is applied to one coil,a magnetic flux is generated to cause an electromotive force in theother coil, and is rapidly being commercialized in small devices such asmobile phones. The magnetic induction method may transfer power of up toseveral hundreds of kilowatts (kW) and has high efficiency. However,since a maximum transmission distance is 1 centimeter (cm) or less, adevice to be charged should be located adjacent to a charger or thefloor.

The electromagnetic resonance method uses an electric field or amagnetic field instead of using electromagnetic waves or current. Theelectromagnetic resonance method is rarely influenced by electromagneticwaves and thus is advantageously safe for other electronic devices orhuman bodies. In contrast, this method may be used in a limited distanceand space and energy transmission efficiency is somewhat low.

The short-wavelength wireless power transmission method (briefly,referred to as the RF transmission method) takes advantage of the factthat energy may be directly transmitted and received in the form of aradio wave. This technology is a RF wireless power transmission methodusing a rectenna. The rectenna is a combination of an antenna and arectifier and means an element for directly converting RF power into DCpower. That is, the RF method is technology of converting AC radio wavesinto DC. Recently, as efficiency of the RF method has been improved,studies into commercialization of the RF method have been activelyconducted.

Wireless power transmission technology may be used not only in mobilerelated industries but also in various industries such as IT, railroadand home appliance.

If a conductor which is not a wireless power receiver, that is, aforeign object (FO), is present in a wireless charging area, anelectromagnetic signal received from a wireless power transmitter may beinduced in the FO, thereby increasing in temperature. For example, theFO may include coins, clips, pins, and ballpoint pens.

If an FO is present between a wireless power receiver and a wirelesspower transmitter, wireless charging efficiency may be significantlylowered, and the temperatures of the wireless power receiver and thewireless power transmitter may increase due to increase in ambienttemperature of the FO. If the FO located in the charging area is notremoved, power waste may occur and the wireless power transmitter andthe wireless power receiver may be damaged due to overheating.

Accordingly, accurate detection of the FO located in the charging areais becoming an important issue in wireless charging technology.

Technical Problem

Embodiments provide a method of detecting a foreign object for wirelesscharging, and an apparatus and system therefor.

Embodiments provide a foreign object detection method capable of moreaccurately detecting a foreign object, by dynamically calibrating ameasured quality factor value upon detecting the foreign objectaccording to shift of a current peak frequency from a reference peakfrequency, and an apparatus therefor.

Embodiments provide a foreign object detection method capable of moreaccurately detecting a foreign object, by calculating a quality factorslope based on output voltage levels measured at a current peakfrequency and a start frequency within an operating frequency band andcomparing the quality factor slope with a predetermined quality factorslope threshold value, and an apparatus and system therefor.

Embodiments provide a foreign object detection method capable of moreaccurately detecting a foreign object, by calculating a quality factorslope based on quality factor values measured at a current peakfrequency and a start frequency within an operating frequency band andcomparing the quality factor slope with a predetermined quality factorslope threshold value, and an apparatus and system therefor.

Embodiments provide a foreign object detection method capable ofimproving foreign object detection capability, by adaptively applying aforeign object detection method based on a quality factor and a foreignobject detection method based on a peak frequency, and an apparatus andsystem therefor.

Embodiments provide a foreign object detection method capable ofdetecting a foreign object based on the shift direction of a peakfrequency, and an apparatus and system therefor.

The technical problems solved by the embodiments are not limited to theabove technical problems and other technical problems which are notdescribed herein will become apparent to those skilled in the art fromthe following description.

Embodiments provide a method of detecting a foreign object, and anapparatus and system therefor.

In an embodiment, a method of detecting a foreign object in a wirelesspower transmitter includes measuring a quality factor valuecorresponding to a reference operating frequency when an object isdetected, searching for a current peak frequency having a maximumquality factor value within an operating frequency band, receiving aforeign object detection status packet including information on areference peak frequency from a wireless power receiver, calibrating themeasured quality factor value using a difference between the currentpeak frequency and the reference peak frequency, and comparing thecalibrated quality factor value with a predetermined quality factorthreshold value to determine whether the foreign object is present.

The foreign object detection status packet may further include areference quality factor value. The quality factor threshold value maybe determined based on the reference quality factor value, and thereference quality factor value may be measured at the referenceoperating frequency in a state in which the wireless power receiver ispowered off.

The reference peak frequency may have a maximum quality factor valuewithin the operating frequency band in a state in which only thewireless power receiver is placed in a charging area.

In addition, the foreign object detection method may further includeidentifying whether the detected object is a receiver capable ofperforming wireless power transfer, and the quality factor value may bemeasured in a state in which power transfer is temporarily stoppedbefore entering the identifying step, after detecting the object.

In addition, the foreign object detection method may further includestopping power transfer to the wireless power receiver upon determiningthat the foreign object is detected.

In addition, the foreign object detection method may further includeoutputting a predetermined warning alarm indicating that the foreignobject has been detected after stopping power transfer.

In addition, the foreign object detection method may further includechecking whether the detected foreign object has been removed from thecharging area. Upon checking that the detected foreign object has beenremoved, power transfer to the wireless power receiver may start and thewarning alarm may be released.

The foreign object detection status packet may further include modeinformation, and whether the information on the reference peak frequencyis included in the foreign object detection status packet may beidentified based on the mode information.

In addition, the foreign object detection method may further includereceiving a first maximum quality factor value corresponding to thereference peak frequency from the wireless power receiver, andcalculating a quality factor shift value by subtracting a second maximumquality factor value corresponding to the current peak frequency fromthe first maximum quality factor value. The measured quality factorvalue may be calibrated further using the quality factor shift value.

In addition, the first maximum quality factor value may be included andreceived in the foreign object detection status packet.

The determining of whether the foreign object is present may includedetermining that the foreign object is present, when the calibratedquality factor value is less than the predetermined quality factorthreshold value and determining that the foreign object is not present,when the calibrated quality factor value is equal to or greater than thepredetermined quality factor threshold value.

According to another embodiment, a method of detecting a foreign objectin a wireless power transmitter includes searching for a current peakfrequency having a maximum quality factor value within an operatingfrequency band when an object is detected, measuring output voltagelevels at a start frequency and the current peak frequency of theoperating frequency band, calculating a quality factor slope based onthe calculated quality factor levels, and determining whether theforeign object is present based on the calculated quality factor slope.

The quality factor slope may be calculated by dividing a differencebetween the output voltage level corresponding to the current peakfrequency and the output voltage level corresponding to the startfrequency by a difference between the current peak frequency and thestart frequency.

In addition, the determining of whether the foreign object is presentmay include determining whether the calculated quality factor slope isless than a predetermined quality factor slope threshold value,determining that the foreign object is present, when the calculatedquality factor slope is less than the predetermined quality factor slopethreshold value, and determining that the foreign object is not present,when the calculated quality factor slope is equal to or greater than thepredetermined quality factor slope threshold value.

According to another embodiment, a method of detecting a foreign objectin a wireless power transmitter includes searching for a current peakfrequency having a maximum quality factor value within an operatingfrequency band when an object is detected, deciding a quality factorvalue at a start frequency and the current peak frequency of theoperating frequency band, calculating a quality factor slope based onthe decided quality factor value, and determining whether the foreignobject is present based on the calculated quality factor slope.

The quality factor slope may be calculated by dividing a differencebetween the quality factor value corresponding to the current peakfrequency and the quality factor value corresponding to the startfrequency by a difference between the current peak frequency and thestart frequency.

According to another embodiment, a wireless power transmitter includes aquality factor measurement unit configured to measure a quality factorvalue corresponding to a reference operating frequency when an object isdetected, a peak frequency search unit configured to search for acurrent peak frequency having a maximum quality factor value within anoperating frequency band, a communication unit configured to receive aforeign object detection status packet including information on areference peak frequency from a wireless power receiver, a calibrationunit configured to calibrate the measured quality factor value using adifference between the current peak frequency and the reference peakfrequency, and a detection unit configured to compare the calibratedquality factor value with a predetermined quality factor threshold valueto determine whether the foreign object is present.

The foreign object detection status packet may further include areference quality factor value. The quality factor threshold value maybe determined based on the reference quality factor value, and thereference quality factor value may be measured at the referenceoperating frequency in a state in which the wireless power receiver ispowered off.

The reference peak frequency may have a maximum quality factor valuewithin the operating frequency band in a state in which only thewireless power receiver is placed in a charging area.

In addition, the measurement may measure the quality factor value in astate in which power transfer is temporarily stopped before entering theprocedure of identifying the wireless power receiver and search for thecurrent peak frequency.

In addition, power transfer to the wireless power receiver may bestopped, upon determining that the foreign object is detected.

In addition, the foreign object detection apparatus may further includean alarm unit configured to output a predetermined warning alarmindicating that the foreign object has been detected after stoppingpower transfer.

In addition, the foreign object detection apparatus may further includea controller configured to check whether the detected foreign object hasbeen removed from the charging area. Upon checking that the detectedforeign object has been removed, the controller may perform control tostart power transfer to the wireless power receiver and to release thewarning alarm.

The foreign object detection status packet may further include modeinformation, and whether the information on the reference peak frequencyis included in the foreign object detection status packet may beidentified based on the mode information.

In addition, when a first maximum quality factor value corresponding tothe reference peak frequency is received from the wireless powerreceiver through the communication unit, the calibration unit maycalculate a quality factor shift value by subtracting a second maximumquality factor value corresponding to the current peak frequency fromthe first maximum quality factor value, and calibrate the measuredquality factor value further using the quality factor shift value.

Here, the first maximum quality factor value may be included andreceived in the foreign object detection status packet.

The detection unit may determine that the foreign object is present whenthe calibrated quality factor value is less than the predeterminedquality factor threshold value and determine that the foreign object isnot present when the calibrated quality factor value is equal to orgreater than the predetermined quality factor threshold value.

According to another embodiment, a foreign object detection apparatusfor detecting a foreign object placed in a charging area includes aquality factor measurement unit configured to search for a current peakfrequency having a maximum quality factor value within an operatingfrequency band when an object is detected, an output voltage measurementunit configured to measure output voltage levels at a start frequencyand the current peak frequency of the operating frequency band, aquality factor slope determination unit configured to calculate aquality factor slope based on the calculated quality factor levels, anda foreign object detection unit configured to determine whether theforeign object is present based on the calculated quality factor slope.

According to another embodiment, a foreign object detection apparatusfor detecting a foreign object placed in a charging area includes a peakfrequency search unit configured to search for a current peak frequencyhaving a maximum quality factor value within an operating frequency bandwhen an object is detected, a quality factor measurement unit configuredto measure a quality factor value at a start frequency and the currentpeak frequency of the operating frequency band, a quality factor slopedetermination unit configured to calculate a quality factor slope basedon the measured quality factor value, and a foreign object detectionunit configured to determine whether the foreign object is present basedon the calculated quality factor slope.

In addition, according to an embodiment, it is possible to provide aforeign object detection method capable of improving foreign objectdetection capability, by adaptively applying a foreign object detectionmethod based on a quality factor and a foreign object detection methodbased on a peak frequency, and an apparatus and system therefor.

In addition, according to an embodiment, it is possible to provide aforeign object detection method capable of detecting a foreign objectbased on the shift direction of a peak frequency from the reference peakfrequency, and an apparatus and system therefor.

In another embodiment, a computer-readable recording medium havingrecorded thereon a program for executing any one of the above-describedmethods may be provided.

The aspects of the disclosure are only a part of the preferredembodiments of the disclosure, and various embodiments based ontechnical features of the disclosure may be devised and understood bythe person with ordinary skill in the art based on the detaileddescription of the disclosure.

Advantageous Effects

The effects of the method, apparatus and system according to embodimentsare as follows.

Embodiments provide a method of detecting a foreign object for wirelesscharging, and an apparatus and system therefor.

Embodiments provide a method of detecting a foreign object, which iscapable of more accurately detecting a foreign object, and an apparatusand system therefor.

Embodiments may minimize unnecessary power waste and a heatingphenomenon due to a foreign object.

Embodiments provide a foreign object detection method capable of moreaccurately detecting a foreign object, by dynamically calibrating ameasured quality factor value upon detecting the foreign objectaccording to a degree of shift of a current peak frequency from areference peak frequency, and an apparatus therefor.

Embodiments provide a foreign object detection method capable of moreaccurately detecting a foreign object, by calculating a quality factorslope based on output voltage levels measured at a current peakfrequency and a start frequency in an operating frequency band andcomparing the quality factor slope with a predetermined quality factorslope threshold value, and an apparatus and system therefor.

Embodiments provide a foreign object detection method capable of moreaccurately detecting a foreign object, by calculating a quality factorslope based on quality factor values measured at a current peakfrequency and a start frequency in an operating frequency band andcomparing the quality factor slope with a predetermined quality factorslope threshold value, and an apparatus and system therefor.

Embodiments provide a foreign object detection method capable ofimproving foreign object detection capability, by adaptively applying aforeign object detection method based on a quality factor and a foreignobject detection method based on a peak frequency, and an apparatus andsystem therefor.

Embodiments provide a foreign object detection method capable ofdetecting a foreign object based on the shift direction of a peakfrequency, and an apparatus and system therefor.

The effects of the disclosure are not limited to the above-describedeffects and other effects which are not described herein may be derivedby those skilled in the art from the following description of theembodiments of the disclosure. That is, effects which are not intendedby the disclosure may be derived by those skilled in the art from theembodiments of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a wireless charging systemaccording to an embodiment;

FIG. 2 is a block diagram illustrating a wireless charging systemaccording to another embodiment;

FIG. 3 is a view illustrating a sensing signal transmission procedure ina wireless charging system according to an embodiment;

FIG. 4 is a state transition diagram explaining a wireless powertransmission procedure according to another embodiment;

FIGS. 5A and 5B are state transition diagrams explaining a wirelesspower transmission procedure according to another embodiment;

FIG. 6 is a block diagram illustrating the structure of a wireless powertransmitter according to an embodiment;

FIG. 7 is a block diagram illustrating the structure of a wireless powerreceiver interworking with a wireless power transmitter according to anembodiment;

FIG. 8 is a diagram illustrating a method of modulating and demodulatinga wireless power signal according to an embodiment;

FIG. 9 is a diagram illustrating a packet format according to anembodiment;

FIG. 10 is a diagram illustrating types of packets according to anembodiment;

FIGS. 11A and 11B are diagrams illustrating the structure of a foreignobject detection apparatus according to an embodiment;

FIG. 12 is a block diagram illustrating the structure of a foreignobject detection apparatus according to another embodiment;

FIGS. 13A to 13D are state transition diagrams explaining foreign objectdetection in a foreign object detection apparatus according to anembodiment;

FIGS. 14A to 14B are views illustrating the structure of a foreignobject detection (FOD) status packet message according to an embodiment;

FIG. 15 is a diagram showing the structure of an FOD status packetmessage according to another embodiment;

FIG. 16 is a flowchart illustrating a foreign object detection method ina wireless power transmission apparatus according to an embodiment;

FIG. 17 is an experimental result table illustrating a reference peakfrequency of each receiver type and change in peak frequency accordingto placement of a foreign object;

FIG. 18 is an experimental result graph showing change in quality factorvalue and peak frequency according to placement of a foreign object in awireless charging system according to an embodiment;

FIG. 19 is a block diagram illustrating the configuration of a foreignobject detection apparatus according to another embodiment;

FIG. 20 is a view illustrating change in quality factor slope dependingon whether a foreign object is present in a wireless charging systemaccording to an embodiment; and

FIGS. 21A to 21B are flowcharts illustrating a foreign object detectionmethod in a wireless power transmission apparatus according to anembodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A method of detecting a foreign object in a wireless power transmitteraccording to an embodiment includes measuring a quality factor valuecorresponding to a reference operating frequency when an object isdetected, searching for a current peak frequency having a maximumquality factor value within an operating frequency band, receiving aforeign object detection status packet including information on areference peak frequency from a wireless power receiver, calibrating themeasured quality factor value using a difference between the currentpeak frequency and the reference peak frequency, and comparing thecalibrated quality factor value with a predetermined quality factorthreshold value to determine whether the foreign object is present.

Hereinafter, apparatuses and various methods according to embodimentswill be described in detail with reference to the accompanying drawings.In general, a suffix such as “module” or “unit” may be used to refer toelements or components. Use of such a suffix herein is merely intendedto facilitate description of the specification, and the suffix itself isnot intended to have any special meaning or function.

In the following description of the embodiments, it will be understoodthat, when each element is referred to as being formed “on” or “under”the other element, it can be directly “on” or “under” the other elementor be indirectly formed with one or more intervening elementstherebetween. In addition, it will also be understood that “on” or“under” the element may mean an upward direction and a downwarddirection of the element.

In the description of embodiments, an apparatus having a function fortransmitting wireless power in a wireless charging system may be usedinterchangeably with a wireless power transmitter, a wireless powertransfer apparatus, a wireless electric power transfer apparatus, awireless electric power transmitter, a transmission end, a transmitter,a transmission apparatus, a transmission side, a wireless power transferapparatus, a wireless power transferer, etc., for convenience ofdescription. An apparatus having a function for receiving wireless powerfrom a wireless power transfer apparatus may be used interchangeablywith a wireless electric power reception apparatus, a wireless electricpower receiver, a wireless power reception apparatus, a wireless powerreceiver, a reception terminal, a reception side, a reception apparatus,a receiver, etc.

The transmitter according to embodiment may be configured in the form ofa pad, a cradle, an access point (AP), a small base station, a stand, aceiling embedded structure or a wall-mounted structure. One transmittermay transfer power to a plurality of wireless power receptionapparatuses. To this end, the transmitter may include at least onewireless power transfer means. Here, the wireless power transfer meansmay use various wireless power transfer standards based on anelectromagnetic induction method of performing charging using theelectromagnetic induction principle in which a magnetic field isgenerated in a power transfer-end coil and electricity is induced in areception-end coil by the magnetic field. Here, the wireless powertransfer means may include wireless charging technology of theelectromagnetic induction method defined in the Wireless PowerConsortium (WPC) and Power Matters Alliance (PMA) which are the wirelesscharging technology organizations.

In addition, a receiver according to an embodiment may include at leastone wireless power reception means and may simultaneously receivewireless power from two or more transmitters. Here, the wireless powerreception means may include wireless charging technology of theelectromagnetic induction method defined in the Wireless PowerConsortium (WPC) and Power Matters Alliance (PMA) which are the wirelesscharging technology organizations.

The receiver according to the embodiment may be used in a smallelectronic apparatus such as a mobile phone, a smartphone, a laptop, adigital broadcast terminal, a personal digital assistant (PDA), aportable multimedia player (PMP), a navigation system, an MP3 player, anelectric toothbrush, an electronic tag, a lighting device, a remotecontroller, a fishing float, a wearable device such as a smart watch,etc. without being limited thereto, and may be used in any apparatusincluding wireless power reception means according to embodiment tocharge a battery.

FIG. 1 is a block diagram illustrating a wireless charging systemaccording to an embodiment.

Referring to FIG. 1 , the wireless charging system roughly includes awireless power transfer end 10 for wirelessly transmitting power, awireless power reception end 20 for receiving the transmitted power andan electronic apparatus 30 for receiving the received power.

For example, the wireless power transfer end 10 and the wireless powerreception end 20 may perform in-band communication in which informationis exchanged using the same frequency band as the operating frequencyused for wireless power transfer.

In in-band communication, when a power signal 41 transmitted by thewireless power transfer end 10 is received by the wireless powerreception end 20, the wireless power reception end 20 may modulate thereceived power signal and transmit a modulated signal 42 to the wirelesspower transfer end 10.

In another example, the wireless power transfer end 10 and the wirelesspower reception end 20 may perform out-of-band communication in whichinformation is exchanged using the frequency band different from theoperating frequency used for wireless power transfer.

For example, the information exchanged between the wireless powertransfer end 10 and the wireless power reception end 20 may includestatus information of each other and control information. Here, thestatus information and the control information exchanged between thetransmission end and the reception end will become more apparent throughthe following description of the embodiments.

In-band communication and out-of-communication may provide bidirectionalcommunication, but the embodiments are not limited thereto. In anotherembodiment, in-band communication and out-of-communication may provide aunidirectional communication or half duplex communication.

For example, unidirectional communication may, but is not limited to,mean transmission of information from the wireless power reception end20 to the wireless power transfer end 10 or transmission from thewireless power transfer end 10 to the wireless power reception end 20.

The half duplex communication method is characterized in thatbidirectional communication between the wireless power reception end 20and the wireless power transfer end 10 is enabled but information can betransmitted only by one device at a certain point in time.

The wireless power reception end 20 according to the embodiment mayacquire a variety of status information of the electronic apparatus 30.For example, the status information of the electronic apparatus 30 mayinclude, but is not limited to, current power usage information, currentpower usage information, information for identifying an executedapplication, CPU usage information, battery charge status information,battery output voltage/current information, etc. and may includeinformation capable of being acquired from the electronic apparatus 30and being used for wireless power control.

In particular, the wireless power transfer end 10 according to theembodiment may transmit a predetermined packet indicating whether fastcharging is supported to the wireless power reception end 20. Thewireless power reception end 20 may inform the electronic apparatus 30that the wireless power transfer end 10 supports the fast charging mode,upon determining that the wireless power transfer end 10 supports thefast charging mode. The electronic apparatus 30 may display informationindicating that fast charging is possible through a predetermineddisplay means, for example, a liquid crystal display.

In addition, the user of the electronic apparatus 30 may select apredetermined fast charging request button displayed on the liquidcrystal display means and control the wireless power transmission end 10to operate in the fast charging mode. In this case, when the userselects the fast charging request button, the electronic apparatus 30may transmit a predetermined fast charging request signal to thewireless power reception end 20. The wireless power reception end 20 maygenerate and transmit a charging mode packet corresponding to thereceived fast charging request signal to the wireless power transmissionend 10, thereby switching a normal low-power charging mode to the fastcharging mode.

FIG. 2 is a block diagram illustrating a wireless charging systemaccording to another embodiment.

For example, as denoted by reference numeral 200 a, the wireless powerreception end 20 may include a plurality of wireless power receptionapparatuses and one wireless power transmission end 10 may be connectedwith a plurality of wireless power reception apparatuses to performwireless charging. At this time, the wireless power transmission end 10divides and transmits power to the plurality of wireless power receptionapparatuses in a time-divisional manner, without being limited thereto.In another example, the wireless power transmission end 10 may divideand transmit power to the plurality of wireless power receptionapparatuses using different frequency bands allocated to the wirelesspower reception apparatuses.

At this time, the number of wireless power reception apparatusesconnectable to one wireless power transmission apparatus 10 may beadaptively determined based on at least one of the required power amountof each wireless power reception apparatus, a battery charging status,the power consumption of an electronic apparatus and the available poweramount of the wireless power transmission apparatus.

In another example, as denoted by reference numeral 200 b, the wirelesspower transmission end 10 may include a plurality of wireless powertransmission apparatuses. In this case, the wireless power reception end20 may be simultaneously connected to the plurality of wireless powertransmission apparatuses to simultaneously receive power from theconnected wireless power transmission apparatuses, thereby performingcharging. At this time, the number of wireless power transmissionapparatuses connected to the wireless power reception end 20 may beadaptively determined based on the required power amount of the wirelesspower reception end 20, the battery charging state, the powerconsumption of the electronic apparatus and the available power amountof the wireless power transmission apparatus.

In addition, the plurality of wireless power transmission apparatusesmay transmit power to the plurality of wireless power receptionapparatuses. At this time, one wireless power transmission apparatustransmits power to one wireless power reception apparatus.

FIG. 3 is a view illustrating a sensing signal transmission procedure ina wireless charging system according to an embodiment.

For example, a wireless power transmitter may include three transmissioncoils 111, 112 and 113 mounted therein. The transmission coils maypartially overlap each other, and the wireless power transmittersequentially transmits predetermined sensing signals 117 and 127 fordetecting presence of a wireless power receiver, for example, digitalping signals, through each transmission coil in a predefined order.

As shown in FIG. 3 , the wireless power transmitter may sequentiallytransmit the sensing signal 117 through a primary sensing signaltransmission procedure denoted by reference numeral 110 and identify thetransmission coils 111 and 112, through which a signal strengthindicator 116 is received from the wireless power receiver 115.Subsequently, the wireless power transmitter may perform control tosequentially transmit the sensing signal 127 through a secondary sensingsignal transmission procedure denoted by reference numeral 120, toidentify a transmission coil having good power transfer efficiency (orcharging efficiency), that is, a good alignment state between thetransmission coil and the reception coil, between the transmission coils111 and 112, through which the signal strength indicator 126 isreceived, and to transmit power through the identified transmissioncoil, that is, to perform wireless charging.

As shown in FIG. 3 , the wireless power transmitter performs two sensingsignal transmission procedures in order to more accurately identify towhich transmission coil the reception coil of the wireless powerreceiver is well aligned.

If the signal strength indicators 116 and 126 are received through thefirst transmission coil 111 and the second transmission coil 112 asdenoted by reference numerals 110 and 120 of FIG. 3 , the wireless powertransmitter selects the best aligned transmission coil based on thesignal strength indicator 126 received through the first transmissioncoil 111 and the second transmission coil 112, and performs wirelesscharging using the selected transmission coil.

FIG. 4 is a state transition diagram explaining a wireless powertransfer procedure defined in the WPC standard.

Referring to FIG. 4 , power transfer from the transmitter to thereceiver may be broadly divided into a selection phase 410, a ping phase420, an identification and configuration phase 430, and a power transferphase 440.

The selection phase 410 may transition when power transfer starts orwhen a specific error or a specific event is sensed while power transferis maintained. The specific error and the specific event will becomeapparent from the following description.

In addition, in the selection phase 410, the transmitter may monitorwhether an object is present on a charging interface surface. Upondetecting that the object is placed on the charging interface surface,the transmitter may transition to the ping phase 420 (S401).

In the selection phase 410, the transmitter may transmit an analog pingsignal having a very short pulse and may detect whether an object ispresent in an active area, that is, a chargeable area, of the charginginterface surface based on change in current of the transmission coil.

When the object is detected in the ping phase 420, the transmitteractivates, that is, boots, the receiver and transmits a digital ping foridentifying whether the object is a receiver. When a response signal,for example, a signal strength indicator, is not received from thereceiver in response to the digital ping in the ping phase 410, thetransmitter may transition to the selection phase 410 again (S402). Inaddition, when a signal indicating that power transfer has ended, thatis, a charging end signal, is received from the receiver in the pingphase 420, the transmitter may transition to the selection phase 410(S403).

When the ping phase 420 has ended, the transmitter may identify thereceiver and transition to the identification and configuration phase430 for identifying the receiver and collecting the configuration andstatus information of the receiver (S404).

In the identification and configuration phase 430, when an unexpectedpacket is received, when an expected packet is not received during apredetermined time (timeout), when a packet transmission error occurs,or when power transfer contract is not established (no power transfercontract), the transmitter may transition to the selection phase 410(S405).

If identification and configuration of the receiver has ended, thetransmitter may transition to the power transfer phase 440 fortransferring wireless power (S406).

In the power transfer phase 440, when an unexpected packet is received,when an expected packet is not received during a predetermined time(timeout), when power transfer contract violation occurs or whencharging is terminated, or when charging has ended, the transmitter maytransition to the selection phase 410 (S407).

In addition, in the power transfer phase 440, if a power transfercontract needs to be reconfigured according to transmitter statuschange, etc., the transmitter may transition to the identification andconfiguration phase 430 (S408).

The power transfer contract may be configured based on the transmitterand receiver status information and characteristic information. Forexample, the transmitter status information may include information onthe maximum amount of transmittable power, information on the maximumnumber of receivable receivers, etc. and the receiver status informationmay include information on required power.

FIGS. 5A and 5B are state transition diagrams explaining a wirelesspower transfer procedure.

Referring to FIG. 5A, power transfer from the transmitter to thereceiver according to the embodiment may be broadly divided into aselection phase 510, a ping phase 520, an identification andconfiguration phase 530, a negotiation phase 540, a calibration phase550, a power transfer phase 560 and a renegotiation phase 570.

The selection phase 510 may transition when power transfer starts orwhen a specific error or a specific event is sensed while power transferis maintained (for example, including reference numerals S502, S504,S508, S510 and S512). The specific error and the specific event willbecome apparent from the following description. In addition, in theselection phase 510, the transmitter may monitor whether an object ispresent on an interface surface. Upon detecting that the object ispresent on the interface surface, the transmitter may transition to theping step 520. In the selection phase 510, the transmitter may transmitan analog ping signal having a very short pulse and detect whether anobject is present in an active area of the interface surface based onchange in current of a transmission coil or a primary coil.

If the object is detected in the selection phase 510, the wireless powertransmitter may measure the quality factor of a wireless power resonantcircuit (e.g., a power transfer coil and/or a resonant capacitor).

In one embodiment, when the object is detected in the selection phase510, the quality factor may be measured in order to determine whetherthe wireless power receiver is placed in the charging area along with aforeign object. The coil provided in the wireless power transmitter hasan inductance and/or a series resistance component in the coil which maydecrease due to environmental change, thereby decreasing the qualityfactor value. In order to determine whether the foreign object ispresent using the measured quality factor value, the wireless powertransmitter may receive, from the wireless power receiver, a referencequality factor value previously measured in a state in which a foreignobject is not placed in the charging area. The reference quality factorvalue received in the negotiation phase 540 may be compared with themeasured quality factor value, thereby determining whether the foreignobject is present. However, in the case of a wireless power receiverhaving a low reference quality factor (for example, a specific wirelessreceiver may have a low reference quality factor value according to thetype, usage and characteristics of the wireless power receiver), since adifference between the quality factor value measured when the foreignobject is present and the reference quality factor is small, it isdifficult to determine whether a foreign object is present. Accordingly,it is necessary to further consider other determination elements or todetermine whether a foreign object is present using other methods.

In another embodiment, when the object is detected in the selectionphase 510, the quality factor value within a specific frequency region(e.g., an operating frequency region) may be measured in order todetermine whether the wireless power receiver is placed in the chargingarea along with the foreign object. The coil of the wireless powertransmitter may have the inductance and/or series resistance componentin the coil which may decrease due to environmental change, therebychanging (shifting) the resonant frequency of the coil of the wirelesspower transmitter. That is, a quality factor peak frequency as afrequency at which the maximum quality factor value is measured in theoperating frequency band may be shifted.

For example, since the wireless power receiver includes a magneticshield (shielding material) having high permeability, the highpermeability may increase the inductance value measured in the coil ofthe wireless power transmitter. In contrast, a foreign object, which isa metallic material, decreases the inductance value.

For example, in the case where the resonant frequency of the coil of thewireless power transmitter is 100 kHz, a graph showing change in qualityfactor value measured when the wireless power receiver or the foreignobject is placed in the charging area is shown in FIG. 5B.

Referring to FIG. 5B, generally, in the case of an LC resonant circuit,the resonant frequency f resonant is calculated by ½π√{square root over(L*C)}.

Referring to the left graph of FIG. 5B, when only the wireless powerreceiver is placed in the charging area, since the L value increases,the resonant frequency decreases to be moved (shifted) to the left onthe frequency axis.

Referring to the right graph of FIG. 5B, when a foreign object is placedin the charging area, since the L value decreases, the resonantfrequency increases to be moved (shifted) to the right on the frequencyaxis.

In order to determine whether a foreign object is present using afrequency at which a maximum quality factor is measured, that is, ameasured peak frequency, the wireless power transmitter may receive thereference maximum quality factor frequency pre-measured in a state inwhich the foreign object is not placed in the charging area, that is,the reference peak frequency, from the wireless power receiver. Thereceived reference peak frequency value may be compared with themeasured peak frequency value in the negotiation phase 540, therebydetermining whether a foreign object is present.

The foreign object detection through peak frequency comparison may beused along with a method of comparing quality factor values. If adifference between the reference quality factor value and the measuredquality factor value is small, for example, if the difference is equalto or less than 10%, presence of the foreign object may be determined bycomparing the reference peak frequency with the measured peak frequency.In contrast, if the difference between the quality factors exceeds 10%,the wireless power transmitter may immediately determine that theforeign object is present.

In another example, upon determining that the foreign object is notpresent as the result of comparing the reference quality factor valuewith the measured quality factor value, the reference peak frequency maybe compared with the measured peak frequency to determine whether aforeign object is present. If it is difficult to detect the foreignobject using the quality factor, the wireless power receiver may includeinformation on the reference peak frequency in a foreign objectdetection status packet and transmit the packet to the wireless powertransmitter, and the wireless power transmitter may detect the foreignobject further using information on the reference peak frequency,thereby improving foreign object detection capability.

The comparison method of the reference quality factor will be describedin detail in the following embodiment.

In the ping step 520, when the object is sensed, the transmitter wakesup the receiver and transmits a digital ping for identifying whether thedetected object is a wireless power receiver. In the ping step 520, whena response signal to the digital ping, for example, a signal strengthpacket, is not received from the receiver, the transmitter maytransition to the selection phase 510 again. In addition, in the pingphase 520, when a signal indicating that power transfer has beenterminated, that is, a charging termination packet, is received from thereceiver, the transmitter may transition to the selection phase 510.

If the ping phase 520 is terminated, the transmitter may transition tothe identification and configuration phase 530 for identifying thereceiver and collecting the configuration and status information of thereceiver.

In the identification and configuration phase 530, when an unexpectedpacket is received, when an expected packet is not received during apredetermined time (timeout), when a packet transmission error occurs,or when power transfer contract is not established (no power transfercontract), the transmitter may transition to the selection phase 510.

The transmitter may determine whether entry into the negotiation phase540 is necessary based on the negotiation field value of theconfiguration packet received in the identification and configurationphase 530.

Upon determining that negotiation is necessary, the transmitter maytransition to the negotiation phase 540 to perform a predetermined FODprocedure.

In contrast, upon determining that negotiation is not necessary, thetransmitter may immediately transition to the power transfer phase 560.

In the negotiation phase 540, the transmitter may receive a foreignobject detection (FOD) status packet including a reference qualityfactor value. Alternatively, an FOD status packet including a referencepeak frequency value may be received. Alternatively, a status packetincluding a reference quality factor value and a reference peakfrequency value may be received. At this time, the transmitter maydetermine a quality factor threshold value for FO detection based on thereference quality factor value. The transmitter may determine a peakfrequency threshold value for FO detection based on the reference peakfrequency value.

The transmitter may detect whether an FO is present in the charging areausing the quality factor threshold value for FO detection and acurrently measured quality factor value (a quality factor value measuredbefore the ping phase) and control power transfer according to theresult of FO detection. For example, when the FO is detected, powertransfer may be stopped, without being limited thereto.

The transmitter may detect whether an FO is present in the charging areausing the peak frequency threshold value for FO detection and acurrently measured quality factor value (a quality factor value measuredbefore the ping phase) and control power transfer according to theresult of FO detection. For example, when the FO is detected, powertransfer may be stopped, without being limited thereto.

When the FO is detected, the transmitter may return to the selectionphase 510. In contrast, when the FO is not detected, the transmitter maytransition to the power transfer phase 560 through the calibration phase550. Specifically, when the FO is not detected, the transmitter maymeasure power loss at the reception end and the transmission end, inorder to determine the strength of the power received by the receptionend and to determine the strength of the power transmitted by thetransmission end in the calibration phase 550. That is, the transmittermay predict power loss based on a difference between the transmissionpower of the transmission end and the reception power of the receptionend in the calibration phase 550. The transmitter according to oneembodiment may calibrate the threshold value for FO detection using thepredicted power loss.

In the power transfer phase 560, when an unexpected packet is received,when an expected packet is not received during a predetermined time(timeout), when power transfer contract violation occurs or whencharging is terminated, the transmitter may transition to the selectionphase 510.

In addition, in the power transfer phase 560, if a power transfercontract needs to be reconfigured according to transmitter statuschange, etc., the transmitter may transition to the renegotiation phase570. At this time, when renegotiation is normally terminated, thetransmitter may return to the power transfer phase 560.

The power transfer contract may be configured based on the transmitterand receiver status information and characteristic information. Forexample, the transmitter status information may include information onthe maximum amount of transmittable power, information on the maximumnumber of receivable receivers, etc. and the receiver status informationmay include information on required power.

FIG. 6 is a block diagram illustrating the structure of a wireless powertransmitter according to an embodiment.

Referring to FIG. 6 , the wireless power transmitter 600 may roughlyinclude a power converter 610, a power transmission unit 620, acommunication unit 630, a controller 640, and a sensing unit 650. Itshould be noted that the components of the wireless power transmitter600 are not mandatory and more or fewer components may be included.

As shown in FIG. 6 , the power converter 610 may perform a function forconverting DC power received from the power supply 660 into AC powerhaving a predetermined strength.

The power converter 610 may include a DC-to-DC converter 611, aninverter 612 and a frequency generator 613. Here, the inverter 612 mayinclude a half bridge inverter or a full bridge inverter. However, theembodiment is not limited thereto and the inverter may be a circuit forconverting DC power into AC power having a specific operating frequency.

The DC-to-DC converter 611 may perform a function for converting the DCpower received from the power supply 650 into DC power having a specificstrength according to a control signal of the controller 640.

At this time, the sensing unit 650 may measure the voltage/current ofthe converted DC power and provide the voltage/current to the controller640. In addition, the sensing unit 650 may measure the internaltemperature of the wireless power transmitter 600 and provide themeasured result to the controller 640, in order to determine whetheroverheating has occurred. For example, the controller 640 may adaptivelyblock power supplied from the power supply 650 based on thevoltage/current value measured by the sensing unit 650 or block supplyof power to the amplifier 612. To this end, a predetermined powerblocking circuit for blocking power supplied to the amplifier 612 orblocking power supplied from the power supply 650 may be furtherprovided on one side of the power converter 610.

The inverter 612 may convert the DC-to-DC converted DC power into ACpower based on a reference AC signal generated by a frequency generator613. At this time, the frequency, that is, operating frequency, of thereference AC signal may be dynamically changed according to the controlsignal of the controller 640. The wireless power transmitter 600according to the embodiment may adjust the operating frequency to adjustthe strength of the transmitted power.

For example, the controller 640 may receive the power reception statusinformation and/or power control signal of the wireless power receiverthrough the communication unit 630, determine the operating frequencybased on the received power reception status information and/or powercontrol signal, and dynamically control the frequency generator 613 togenerate the determined operating frequency.

For example, the power reception status information may include thestrength information of a rectifier output voltage, the strengthinformation of current applied to a reception coil, etc., without beinglimited thereto. The power control signal may include a signal forrequesting power increase, a signal for requesting power decrease, etc.

The power transmission unit 620 may include a multiplexer 621 and atransmission coil unit 622. Here, the transmission coil unit 622 mayinclude first to n-th transmission coils. In addition, the powertransmission unit 620 may further include a carrier generator (notshown) for generating a specific carrier frequency for power transfer.In this case, the carrier generator may generate a specific carrierfrequency for mixing with the output AC power of the inverter 612received through the multiplexer 621.

It should be noted that the frequencies of the AC power transmitted tothe transmission coils are different in the embodiment. In anotherembodiment, the resonant frequencies of the transmission coils may bedifferently set using a predetermined frequency controller including afunction for differently adjusting LC resonant characteristics accordingto the transmission coils.

The multiplexer 621 may perform a switch function for transmitting theAC power to the transmission coil selected by the controller 640. Thecontroller 640 may select a transmission coil to be used for powertransfer to the wireless power receiver based on the received signalstrength indicator of each transmission coil.

When a plurality of wireless power receivers is connected, thecontroller 640 according to the embodiment may transmit power throughtime-division multiplexing of the transmission coils.

For example, when three wireless power receivers, that is, first tothird wireless power receivers, are identified using three transmissioncoils, that is, first to third transmission coils, in the wireless powertransmitter 600, the controller 640 may control the multiplexer 621 totransmit AC power at a specific time slot only through a specifictransmission coil.

At this time, the amount of power transmitted to the wireless powerreceiver may be controlled according to the length of the time slotallocated to each transmission coil. However, this is only an embodimentand the strength of the output DC power of the DC-to-DC converter 611may be controlled during a time slot allocated to each transmission coilto control the transmission power of each wireless power receiver.

The controller 640 may control the multiplexer 621 to sequentiallytransmit sensing signals through the first to n-th transmission coils622 during a primary sensing signal transmission procedure. At thistime, the controller 640 may identify a time when the sensing signalwill be transmitted using a timer 655, and control the multiplexer 621to transmit the sensing signal through the transmission coil when asensing signal transmission time arrives. For example, the timer 650 maytransmit a specific event signal to the controller 640 at predeterminedperiods during the ping transmission phase, and the controller 640 maycontrol the multiplexer 621 to transmit a digital ping through thetransmission coil whenever the event signal is sensed.

In addition, the controller 640 may receive a predetermined transmissioncoil identifier for identifying through which transmission coil a signalstrength indicator has been received from a demodulator 632 during theprimary sensing signal transmission procedure, and the signal strengthindicator received through the transmission coil.

For example, in a secondary sensing signal transmission procedure, thecontroller 640 may control the multiplexer 621 to transmit the sensingsignal only through the transmission coil(s), through which the signalstrength indicator has been received during the primary sensing signaltransmission procedure.

In another example, if there are plural transmission coils, throughwhich the signal strength indicator has been received during the primarysensing signal transmission procedure, the controller 640 may determinea transmission coil, through which a signal strength indicator having alargest value has been received, as a transmission coil, through whichthe sensing signal will be first transmitted in the secondary sensingsignal transmission procedure, and control the multiplexer 621 accordingto the result of determination.

The communication unit 630 may include at least one of a modulator 631and a demodulator 632.

The modulator 631 may modulate the control signal generated by thecontroller 640 and transmit the modulated signal to the multiplexer 621.Here, a modulation method of modulating the control signal may include afrequency shift keying (FSK) modulation method, a Manchester codingmodulation method, a phase shift keying (PSK) modulation method, a pulsewidth modulation method, a differential biphase modulation method, etc.,without being limited thereto.

When the signal received through the transmission coil is detected, thedemodulator 632 may demodulate the detected signal and transmit thedemodulated signal to the controller 640. Here, the demodulated signalmay include a signal strength indicator, an error correction (EC)indicator for power control during wireless power transmission, an endof charge (EOC) indicator, an overvoltage/overcurrent/overheatingindicator, etc. However, the embodiment is not limited thereto andvarious types of status information for identifying the status of thewireless power receiver may be included.

In addition, the demodulator 632 may identify through which transmissioncoil the demodulated signal has been received and provide apredetermined transmission coil identifier corresponding to theidentified transmission coil to the controller 640.

In addition, the demodulator 632 may demodulate the signal receivedthrough the transmission coil 622 and transmit the demodulated signal tothe controller 640. For example, the demodulated signal may include asignal strength indicator. However, the embodiment is not limitedthereto and the demodulated signal may include various types of statusinformation of the wireless power receiver.

For example, the wireless power transmitter 600 may acquire the signalstrength indicator through in-band communication for performingcommunication with the wireless power receiver using the same frequencyused for wireless power transfer.

In addition, the wireless power transmitter 600 may transmit wirelesspower using the transmission coil unit 622 and exchange various types ofcontrol signals and status information with the wireless power receiverthrough the transmission coil unit 622. In another example, it should benoted that the wireless power transmitter 600 may further includeseparate coils corresponding to the first to n-th transmission coils ofthe transmission coil unit 622, and in-band communication with thewireless power receiver may be performed using the separate coils.

Although the wireless power transmitter 600 and the wireless powerreceiver perform in-band communication in the description of FIG. 6 ,this is merely an embodiment and short-range bidirectional communicationmay be performed through a frequency band different from a frequencyband used for wireless power signal transmission. For example, theshort-range bidirectional communication may be any one of low-powerBluetooth communication, RFID communication, UWB communication andZigBee communication.

In addition, although the power transmission unit 620 of the wirelesspower transmitter 600 includes the multiplexer 621 and the plurality oftransmission coils 622 in the description of FIG. 6 , this is merely anembodiment and it should be noted that the power transmission unit 620according to another embodiment may include one transmission coil.

FIG. 7 is a block diagram illustrating the structure of a wireless powerreceiver interworking with the wireless power transmitter shown in FIG.6 .

Referring to FIG. 7 , the wireless power receiver 700 may include areception coil 710, a rectifier 720, a DC-to-DC converter 730, a load740, a sensing unit 750, a communication unit 760, and a main controller770. The communication unit 760 may include a demodulator 761 and amodulator 762.

Although the wireless power receiver 700 shown in the example of FIG. 7is shown as exchanging information with the wireless power transmitter600 through in-band communication, this is merely an embodiment and thecommunication unit 760 according to another embodiment may provideshort-range bidirectional communication through a frequency banddifferent from a frequency band used to transmit a wireless powersignal.

AC power received through the reception coil 710 may be transmitted tothe rectifier 720. The rectifier 720 may convert the AC power into DCpower and transmit the DC power to the DC-to-DC converter 730. TheDC-to-DC converter 730 may convert the strength of the DC power outputfrom the rectifier into a specific strength required by the load 740 andtransmit the converted power to the load 740.

The sensing unit 750 may measure the strength of the DC power outputfrom the rectifier 720 and provide the strength to the main controller770. In addition, the sensing unit 750 may measure the strength ofcurrent applied to the reception coil 710 according to wireless powerreception and transmit the measured result to the main controller 770.In addition, the sensing unit 750 may measure the internal temperatureof the wireless power receiver 700 and provide the measured temperaturevalue to the main controller 770.

For example, the main controller 770 may compare the strength of the DCpower output from the rectifier with a predetermined reference value anddetermine whether overvoltage occurs. Upon determining that overvoltageoccurs, a predetermined packet indicating that overvoltage has occurredmay be generated and transmitted to the modulator 762. The signalmodulated by the modulator 762 may be transmitted to the wireless powertransmitter 600 through the reception coil 710 or a separate coil (notshown).

If the strength of the DC power output from the rectifier is equal to orgreater than the predetermined reference value, the main controller 770may determine that a sensing signal is received and perform control totransmit a signal strength indicator corresponding to the sensing signalto the wireless power transmitter 600 through the modulator 762 uponreceiving the sensing signal. In another example, the demodulator 761may demodulate the AC power signal between the reception coil 710 andthe rectifier 720 or the DC power signal output from the rectifier 720,identify whether a sensing signal is received, and provide theidentified result to the main controller 770. At this time, the maincontroller 770 may perform control to transmit the signal strengthindicator corresponding to the sensing signal through the modulator 762.

FIG. 8 is a diagram illustrating a method of modulating and demodulatinga wireless power signal according to an embodiment.

As denoted by reference numeral 810 of FIG. 8 , the wireless powertransmission end 10 and the wireless power reception end 20 may encodeor decode a packet to be transmitted based on internal clock signalshaving the same period.

Hereinafter, the method of encoding the packet to be transmitted will bedescribed in detail with reference to FIGS. 1 to 8 .

Referring to FIG. 1 , when the wireless power transmission end 10 or thewireless power reception end 20 does not transmit a specific packet, thewireless power signal may be an unmodulated AC signal having a specificfrequency as denoted by reference numeral 41 of FIG. 1 .

In contrast, when the wireless power transmission end 10 or the wirelesspower reception end 20 transmits a specific packet, the wireless powersignal may be an AC signal modulated using a specific modulation methodas denoted by reference numeral 42 of FIG. 1 . For example, themodulation method may include an amplitude modulation method, afrequency modulation method and a frequency and amplitude modulationmethod, a phase modulation method, etc., without being limited thereto.

The binary data of the packet generated by the wireless powertransmission end 10 or the wireless power reception end 20 may besubjected to differential biphase encoding as denoted by referencenumeral 820. Specifically, differential biphase encoding have two statustransitions to encode data bit 1 and have one state transition to encodedata bit 0. That is, data bit 1 is encoded such that transition betweena HI state and a LO state occurs in the rising edge and the falling edgeof the clock signal and data bit 0 is encoded such that transitionbetween the HI state and the LO state occurs in the rising edge of theclock signal.

The encoded binary data may be subjected to a byte encoding schemedenoted by reference numeral 830. Referring to reference numeral 830,the byte encoding scheme according to the embodiment may refer to amethod of inserting, into an encoded 8-bit binary bit stream, a startbit and a stop bit for identifying start and stop of the bit stream anda parity bit for sensing error of the bit stream (byte).

FIG. 9 is a view illustrating a packet format according to anembodiment.

Referring to FIG. 9 , the packet format 900 used for informationexchange between the wireless power transfer end 10 and the wirelesspower reception end 20 may include a preamble 910 field for acquiringsynchronization for demodulation of the corresponding packet andidentifying an accurate start bit of the corresponding packet, a header920 field for identifying the type of a message included in thecorresponding packet, a message 930 field for transmitting the content(or payload) of the corresponding packet, and a checksum 940 field foridentifying whether an error has occurred in the corresponding packet.

A packet reception end may identify the size of the message 930 includedin the corresponding packet based on the value of the header 920.

In addition, the header 920 may be defined for each step of the wirelesspower transfer procedure, and the value of the header 920 may be definedas the same value in different phases of the wireless power transmissionprocedure. For example, referring to FIG. 10 , it should be noted thatthe header value corresponding to end power transfer of the ping phaseand end power transfer of the power transfer phase is 0x02.

The message 930 includes data to be transmitted by the transmission endof the corresponding packet. For example, the data included in themessage 930 field may be a report, a request, or a response, withoutbeing limited thereto.

The packet 900 according to another embodiment may further include atleast one of transmission end identification information for identifyingthe transmission end for transmitting the corresponding packet andreception end identification information for identifying the receptionend for receiving the corresponding packet. The transmission endidentification information and the reception end identification mayinclude IP address information, MAC address information, productidentification information, etc. However, the embodiment is not limitedthereto and information for distinguishing the reception end and thetransmission end in the wireless charging system may be included.

The packet 900 according to another embodiment may further includepredetermined group identification information for identifying areception group if the corresponding packet is received by a pluralityof apparatuses.

FIG. 10 is a view illustrating the types of packets transmitted from thewireless power receiver to the wireless power transmitter according toan embodiment.

Referring to FIG. 10 , the packet transmitted from the wireless powerreceiver to the wireless power transmitter may include a signal strengthpacket for transmitting the strength information of a sensed pingsignal, a power transfer type (end power transfer) for requesting powertransfer end from the transmitter, a power control hold-off packet fortransferring information on a time until actual power is controlledafter a control error packet for control is received, a configurationpacket for transferring configuration information of the receiver, anidentification packet and an extended identification packet fortransmitting receiver identification information, a general requestpacket for transmitting a general request message, a specific requestpacket for transmitting a specific request message, an FOD status packetfor transmitting a reference quality factor value for FO detection, acontrol error packet for controlling power transmitted by thetransmitter, a renegotiation packet for starting renegotiation, a 24-bitreceived power packet for transmitting the strength information of thereceived power, and a charge status packet for transmitting the currentcharging status information of the load.

The packets transmitted from the wireless power receiver to the wirelesspower transmitter may be transmitted using in-band communication usingthe same frequency band as the frequency band used to transmit wirelesspower.

FIG. 11A is a diagram illustrating the basic structure of a foreignobject detection apparatus (circuit) installed in a wireless powertransmitter according to an embodiment.

Referring to FIG. 11A, the foreign object detection apparatus (circuit)1190 may include a power supply 1191, a driving unit 1192, a resonantcapacitor 1193, a transmission coil 1194, a quality factor measurementunit 1195, a demodulator 1196 and a controller 1197.

The power supply 1191 may receive and supply external power to thedriving unit 1192.

The driving unit 1192 may convert the DC power received from the powersupply 1191 into AC power and control the strength of the AC poweraccording to a control signal of the controller 1197. The driving unit1192 may include a frequency oscillator for generating a specificfrequency signal and an inverter for amplifying an AC signal oscillatedby the frequency oscillator.

The driving unit 1192 may change at least one of the frequency(operating frequency), duty ratio and amplitude of the AC signalaccording to the control signal of the controller 1197.

The quality factor measurement unit 1195 may monitor change ininductance (or voltage or current) across the resonant capacitor 1193and measure the quality factor value of the transmission coil. Themeasured current quality factor value may be transmitted to thecontroller 1197.

The demodulator 1196 demodulates the signal received from the wirelesspower receiver and transmits the demodulated signal to the controller1197. For example, the demodulator 1196 may demodulate the FOD statuspacket and transmit the demodulated FOD status packet to the controller1197.

The controller 1197 may receive and store the quality factor valuemeasured by the quality factor measurement unit 1195 in a memory. Inaddition, the controller 1197 may read the stored quality factor valuefrom the memory. The controller 1197 may control the operating frequencyof the driving unit 1192. By controlling the operating frequency of thedriving unit 1192, the quality factor measurement unit 1195 may measurethe quality factor value of each operating frequency. The controller1197 may determine a frequency corresponding to a maximum quality factorvalue, that is, a peak frequency, based on the measured quality factorvalue of each operating frequency.

The controller 1197 may determine a quality factor threshold value forthe wireless power receiver based on at least one of a reference qualityfactor value included in the FOD status packet, the operating frequency(reference peak frequency) corresponding to the maximum quality factorvalue, the operating frequency corresponding to a quality factor valueless than the reference quality factor value by a predetermined value,for example, the operating frequency at which a quality factor valueless than the reference quality factor value by 5% is measured.

The controller 1197 may compare the determined quality factor thresholdvalue with the current quality factor value measured by the qualityfactor measurement unit 1195 and/or determine whether an FO is presentin the charging area based on the received operating frequency(threshold frequency) and the measured or calculated operatingfrequency, for example, the operating frequency (peak frequency)corresponding to the maximum quality factor value or the operatingfrequency at which the quality factor value less than the referencequality factor value by 5% is measured.

The controller 1197 according to another embodiment may measure thequality factor value. In this case, the controller 1197 may measure thequality factor value of each frequency while changing the operatingfrequency within a predetermined operating frequency range. In oneembodiment, the controller 1197 may measure the quality factor valueusing a voltage difference across the resonant capacitor 1193, withoutbeing limited thereto.

The quality factor measurement unit 1195 according to one embodiment mayinclude a circuit configuration for measuring and transmitting thevoltage across the resonant capacitor 1193 to the controller 1197.

The quality factor value measured by the controller 1197 may correspondto the quality factor value of the transmission coil measured using ameasurement apparatus such as an LCR meter for measuring at least one ofthe voltage, current, resistance, impedance, capacitance and qualityfactor value of an electric circuit.

The controller 1197 may continuously perform charging, stop charging andreturning to the selection phase according to the result of determiningwhether the foreign object is present.

FIG. 11B is a diagram illustrating the structure (an extension of FIG.11A) of the foreign object detection apparatus (circuit) in the wirelesspower transmitter according to an embodiment.

Referring to FIG. 11B, the foreign object detection apparatus 1100 mayinclude a power supply 1101, a DC-to-DC converter 1110 (omittable), aninverter 1120, a resonant circuit 1130, a measurement unit 1140, acommunication unit 1160, an alarm unit 1175 (omittable), and acontroller 1180. The foreign object detection apparatus 1100 accordingto the present embodiment may be mounted in the wireless powertransmission apparatus.

The resonant circuit 1130 may include a resonant capacitor 1131 and aninductor or a transmission coil 1132 or a transmission antenna, and thecommunication unit 1160 may include at least one of a demodulator 1161and a modulator 1162.

The power supply 1101 may receive DC power through an external powerterminal and transmit the DC power to the DC-to-DC converter 1110.

The DC-to-DC converter 1110 may convert the strength of the DC powerreceived from the power supply 1101 into a specific strength of DC powerunder control of the controller 1180. For example, the DC-to-DCconverter 1110 may include a variable voltage generator capable ofadjusting the strength of the voltage, without being limited thereto.

The inverter 1120 may convert the converted DC power into AC power. Theinverter 1120 may convert the DC power signal input through control of aplurality of switches into an AC power signal and output the AC powersignal.

For example, the inverter 1120 may include a full bridge circuit.However, the embodiment is not limited thereto and the inverter mayinclude a half bridge circuit.

In another example, the inverter 1120 may include a half bridge circuitand a full bridge circuit. In this case, the controller 1180 maydynamically determine whether the inverter 1120 operates as a halfbridge or a full bridge.

The wireless power transmission apparatus according to one embodimentmay adaptively control the bridge mode of the inverter 1120 according tothe strength of the power required by the wireless power receptionapparatus. Here, the bridge mode includes a half bridge mode and a fullbridge mode. For example, if the wireless power reception apparatusrequests low power of 5 W, the controller 1180 may perform control suchthat the inverter 1120 is driven in the half bridge mode. In contrast,if the wireless power reception apparatus requests high power of 15 W,the controller 1180 may perform control such that the inverter is drivenin the full bridge mode.

In another example, the wireless power transmission apparatus mayadaptively determine the bridge mode according to a sensed temperatureand drive the inverter 1120 in the determined bridge mode. If thetemperature of the wireless power transmission apparatus exceeds apredetermined reference value while wireless power is transmitted usingthe half bridge mode, the controller 1180 may perform control todeactivate the half bridge mode and activate the full bridge mode. Thatis, the wireless power transmission apparatus may increase the voltageand decrease the strength of current flowing in the resonant circuit1130 through the full bridge circuit for transmission of power havingthe same strength, thereby maintaining the internal temperature of thewireless power transmission apparatus at a reference value or less.

In general, the amount of heat generated in an electronic part mountedin the electronic apparatus may be more sensitive to the strength ofcurrent than the strength of the voltage applied to the electronic part.

In addition, the inverter 1120 may not only convert the DC power into ACpower but also change the strength of the AC power.

For example, the inverter 1120 may adjust the strength of the output ACpower by adjusting the frequency of a reference alternating currentsignal used to generate the AC power under control of the controller1180. To this end, the inverter 1120 may include a frequency oscillatorfor generating the reference alternating current signal having aspecific frequency. However, this is merely an example and the frequencyoscillator may be mounted independently of the inverter 1120 and mountedat one side of the foreign object detection apparatus 1100.

In another example, the foreign object detection apparatus 1100 mayfurther include a gate driver (not shown) for controlling the switchprovided in the inverter 1120. In this case, the gate driver may receiveat least one pulse width modulation signal from the controller 1180 andcontrol the switch of the inverter 1120 according to the received pulsewidth modulation signal. The controller 1180 may control the duty cycle,that is, the duty rate, and phase of the pulse width modulation signalto control the strength of the output power of the inverter 1120. Thecontroller 1180 may adaptively control the duty cycle and phase of thepulse width modulation signal based on the feedback signal received fromthe wireless power reception apparatus.

The measurement unit 1140 may measure at least one of a voltage, currentand impedance of the resonant capacitor 1131 according to the controlsignal of the controller 1180 to measure or calculate the quality factorvalue and/or peak frequency value of the resonant circuit 1130. At thistime, the calculated quality factor value and/or inductance value may besent to the controller 1180, and the controller 1180 may store thequality factor value and/or the peak frequency value received from themeasurement unit 1140 in a predetermined recording region.

The measurement unit 1140 may measure and store the quality factor valuecorresponding to a predetermined reference operating frequency, that is,a reference measured quality factor value, according to a control signalof the controller 1180.

Alternatively, the measurement unit 1140 may measure the quality factorvalue of each frequency within a specific operating frequency rangeaccording to a control signal of the controller 1180. The controller1180 may determine a peak frequency value corresponding to a maximumquality factor value and store the peak frequency value in the memory.

When an object is detected, the controller 1180 according to theembodiment may control the measurement unit 1140 to measure the qualityfactor values at a plurality of frequencies within the operatingfrequency band before entering the ping phase. The controller 1180 mayidentify a frequency corresponding to a largest value among the measuredquality factor values and determine the identified frequency as acurrent peak frequency.

When the FOD status packet is received from the modulator 1162 in thenegotiation phase, the controller 1180 may determine a threshold value(or a threshold range) for determining whether a foreign object ispresent based on information included in the FOD status packet. Here,the threshold value may include at least one of the peak frequency valueand the quality factor threshold value. If the determined value is athreshold range, the threshold range may include at least one of a peakfrequency threshold range and a quality factor threshold range.

Here, the FOD status packet may include at least one of a referencequality factor value corresponding to the wireless power receiver and/ora reference peak frequency F_reference_peak value.

The controller 1180 may determine the quality factor threshold valueand/or the peak frequency threshold value for determining whether theforeign object is present based on the received reference quality factorvalue and the reference peak frequency value. For example, although avalue corresponding to 90% of the reference quality factor value may bedetermined as the quality factor threshold value, the embodiment is notlimited thereto and the ratio applied to determine the threshold valuemay be differently defined according to the design of those skilled inthe art.

The controller 1180 may calibrate the reference measured quality factorvalue Q_measured_reference based on a difference between the currentpeak frequency F_current_peak value and a reference peak frequencyF_reference_peak value. For example, as a value obtained by subtractingthe reference peak frequency value from the current peak frequency valueincreases, the reference measured quality factor value may increase. Tothis end, a specific calibration function using the difference betweenthe current peak frequency F_current_peak and the reference peakfrequency F_reference_peak as a factor may be predefined. For example,the calibration function may be a linear function. However, theembodiment is not limited thereto and a nonlinear function such as anexponential function may be defined. In another example, a qualityfactor calibration value corresponding to a degree of shift of thecurrent peak frequency from the reference peak frequency may beconfigured and maintained in the form of a table in a predeterminedrecording region of the foreign object detection apparatus 1100.

The controller 1180 may compare the calibrated reference measuredquality factor value with the determined quality factor threshold valueto detect the foreign object placed in the charging area.

For example, the controller 1180 may determine that the foreign objectis present in the charging area when the calibrated reference measuredquality factor value is less than the determined quality factorthreshold value. In contrast, the controller 1180 may determine that theforeign object is not present in the charging area when the calibratedreference measured quality factor value is equal to or greater than thedetermined quality factor threshold value.

In addition, the controller 1180 may calibrate the quality factorthreshold value based on the difference between the current peakfrequency F_current_peak value and the reference peak frequencyF_reference_peak value. The controller 1180 may perform calibration,such that the quality factor threshold value increases as the valueobtained by subtracting the reference peak frequency from the currentpeak frequency value increases. The controller 1180 may compare thequality factor threshold value with the measured quality factor value todetect the foreign object placed in the charging area.

The controller 1180 may stop power transfer upon determining that theforeign object is present and control the alarm unit 1175 to output apredetermined warning alarm indicating that the foreign object has beendetected. For example, the alarm unit 1175 may include, but is notlimited to, a beeper, an LED lamp, a vibration element, a liquid crystaldisplay, etc. However, the embodiment is not limited thereto and apredetermined alarm unit configured to inform the user that the foreignobject has been detected may be provided.

The reference quality factor value included in the FOD status packet maybe determined to be the smallest value of the quality factor valuescalculated in correspondence with the wireless power receiver at aspecific position of a charging bed of a wireless power transmitterspecified for standard performance test.

In addition, if the foreign object is detected in the negotiation phase,the controller 1180 may return to the selection phase and control themeasurement unit 1140 to measure the quality factor value at a specificoperating frequency and/or the peak frequency in the operating frequencyband at predetermined periods. At this time, the controller 1180 mayperform comparison with a predetermined threshold value in a state inwhich the foreign object is detected, thereby determining whether thedetected foreign object has been removed.

Upon determining that the foreign object has been removed, thecontroller 1180 may enter the power transfer phase to perform chargingof the wireless power reception device. The demodulator 1161 demodulatesan in-band signal received from the wireless power reception apparatusand transmits the demodulated signal to the controller 1180. Forexample, the demodulator 1161 may demodulate the FOD status packet ofFIG. 14 or 15 and transmit the demodulated FOD status packet to thecontroller 1180.

As described above, the foreign object detection apparatus 1100according to the disclosure adaptively calibrates the measured qualityfactor value based on the degree of shift of the peak frequency when theobject is detected in the selection phase, thereby remarkably decreasinga probability of foreign object detection failure.

FIG. 12 is a block diagram illustrating the structure of a foreignobject detection apparatus according to another embodiment.

Referring to FIG. 12 , the foreign object detection apparatus 1200 mayinclude a measurement unit 1210, a search unit 1220, a communicationunit 1230, a determination unit 1240, a calibration unit 1250, adetection unit 1260, a storage unit 1270 and a controller 1280. Itshould be noted that the components of the foreign object detectionapparatus 1200 are not mandatory and more or fewer components may beincluded.

Upon detecting that an object has been placed in the charging area inthe selection phase, the measurement unit 1210 may temporarily stoppower transfer and measure the quality factor value at a predeterminedreference operating frequency. For convenience of description,hereinafter, a current quality factor value measured at the referenceoperating frequency is referred to as a measured quality factor valueQ_measured. The reference operating frequency may be set to a specificfrequency included in the operating frequency band. For example, if thewireless power transmission apparatus in which the foreign objectdetection apparatus 1200 is installed supports the WPC standard, thereference operating frequency may be 100 kHz. However, it should benoted that the embodiment is not limited thereto and the referenceoperating frequency may be differently defined according to the appliedstandard.

Upon detecting that an object has been placed in the charging area inthe selection phase, the search unit 1220 may temporarily stop powertransfer and search for a frequency having a maximum quality factorvalue in the operating frequency band. Here, a frequency search offsetfor searching for the frequency having the maximum quality factor valuemay be set in units of 10 kHz*k (k being a natural number), withoutbeing limited thereto. For convenience of description, hereinafter, afrequency having a maximum quality factor value in an operatingfrequency band searched after detecting an object is referred to as acurrent peak frequency F_current_peak. In contrast, a frequency having amaximum quality factor value acquired through a preliminary experimentin a state in which only a wireless power receiver is placed in acharging area is referred to as a reference peak frequencyF_reference_peak.

If a foreign object is placed in the charging area in addition to thewireless power receiver, the frequency having the maximum quality factorvalue searched within the operating frequency band may have a greatervalue than the reference peak frequency acquired when only the wirelesspower receiver is placed in the charging area.

The measured quality factor value measured by the measurement unit 1210and the current peak frequency value searched by the search unit 1220may be stored in a predetermined recording region of the storage unit1270.

The communication unit 1230 may receive a foreign object detection (FOD)status packet from the wireless power receiver in the negotiation phase.Here, the foreign object detection status packet may include at leastone of information on the reference peak frequency value and informationon the reference quality factor value. The structure of the foreignobject detection status packet will become apparent through thedescription of FIGS. 14 to 15 .

The determination unit 1240 may determine a quality factor thresholdvalue for determining whether a foreign object is present based on thereference quality factor value included in the foreign object detectionstatus packet. For example, the quality factor threshold value may beset to a value less than the reference quality factor value by 10%.However, this is merely an embodiment and other ratios may be appliedaccording to the design purpose of a person skilled in the art.

The calibration unit 1250 may calibrate the quality factor thresholdvalue Q_threshold based on a difference between a current peak frequencyF_current_peak and a reference peak frequency F_reference_peak. Forexample, as a value obtained by subtracting the reference peak frequencyvalue from the current peak frequency value increases, the qualityfactor threshold value may increase. To this end, a specific calibrationfunction using the difference between the current peak frequencyF_current_peak and the reference peak frequency F_reference_peak asfactors may be predefined. For example, the calibration function may bea linear function. However, the embodiment is not limited thereto and anonlinear function such as an exponential function may be defined.

The calibration unit 1250 according to another embodiment may set thecalibration amount of the reference measured quality factor value basedon not only the difference between the current peak frequencyF_current_peak and the reference peak frequency F_reference_peak butalso the reference quality factor value. For example, as a valueobtained by subtracting the reference peak frequency value from thecurrent peak frequency value increases, the calibration amount of thequality factor threshold value may increase.

Hereinafter, for convenience of description, the quality factorthreshold value calibrated by the calibration unit 1250 may be referredto as a calibrated quality factor threshold value Q_threshold fixed.

The detection unit 1260 may compare the quality factor threshold valuedetermined by the determination unit 1240 with the calibrated qualityfactor threshold value calculated by the calibration unit 1250 todetermine whether a foreign object is present in the charging area. Forexample, when the current quality factor value is less than thecalibrated quality factor threshold value, the detection unit 1260 maydetermine that the foreign object is present in the charging area. Incontrast, when the current quality factor value is equal to or greaterthan the calibrated quality factor threshold value, the detection unit1260 may determine that the foreign object is not present in thecharging area.

The control unit 1280 may control overall operation of the foreignobject detection apparatus 1200 and, particularly, may control operationof the sub-components according to the wireless power transfer phase.The sub-components include the measurement unit 1210, the search unit1220, the communication unit 1230, the determination unit 1240, thecalibration unit 1250 and the detection unit 1260.

In general, the reference quality factor value measured at the referenceoperating frequency may vary according to the type of the wireless powerreception apparatus. In addition, the frequency value having the maximumquality factor value in the operating frequency band may vary accordingto the type of the wireless power reception apparatus.

Accordingly, the foreign object detection apparatus 1200 may receive thereference quality factor value and the reference peak frequency valuecorresponding to the wireless power reception apparatus through theforeign object detection (FOD) status packet.

As described above, when an object is detected in the selection phase,the foreign object detection apparatus 1200 according to the disclosuremay adaptively calibrate the measured quality factor value according tothe degree of shift of the peak frequency, thereby remarkably decreasinga probability of foreign object detection failure.

FIG. 13A is a state transition diagram explaining foreign objectdetection in a foreign object detection apparatus according to anembodiment.

Referring to FIG. 13A, when the object is detected in the selectionphase 1310, the foreign object detection apparatus may measure thecurrent quality factor value at the reference operating frequency, thatis, the measured quality factor value Q_measured.

In addition, when the object is detected in the selection phase 1310,the foreign object detection apparatus may measure the quality factorvalues at a plurality of frequencies before entering the ping phase 1320and search for a frequency having a maximum quality factor value, thatis, a current peak frequency F_current_peak.

In the ping phase 1320, the foreign object detection apparatus mayperiodically transmit a predetermined power signal for identifying thewireless power receiver, for example, a digital ping.

The foreign object detection apparatus may store information on themeasured quality factor values and the current peak frequency value inthe predetermined recording region.

When a signal strength indicator is received in the ping phase 1320, theforeign object detection apparatus may enter the identification andconfiguration phase 1330 to identify the wireless power receiver and toset various configuration parameters for the identified wireless powerreceiver.

When identification and configuration of the wireless power receiverend, the foreign object detection apparatus may enter the negotiationphase 1340 to perform a foreign object detection procedure.

The foreign object detection procedure may be performed through thefollowing four steps.

In step 1, the foreign object detection apparatus may receive at leastone foreign object detection status packet from the identified wirelesspower receiver. Here, the foreign object detection status packet mayinclude at least one of information on the reference peak frequencyvalue and information on the reference quality factor value.

The information on the reference quality factor value may mean a qualityfactor value measured at a reference operating frequency in a state inwhich the wireless power receiver is powered off. Powering off thereceiver may mean a state in which power is not transmitted to a load.The information on the reference peak frequency value may mean afrequency having a maximum quality factor within the operating frequencyband in a state in which only the wireless power receiver is placed inthe charging area of a predetermined wireless power transmitter. Thewireless power receiver may store a reference peak frequency value inadvance and transmit the reference peak frequency value to the wirelesspower transmitter in the negotiation phase.

In step 2, the foreign object detection apparatus may determine aquality factor threshold value for determining whether a foreign objectis present based on the received reference quality factor value.

In step 3, the foreign object detection apparatus may calibrate (orcompensate for) the reference measured quality factorQ_measured_reference value based on a difference between the currentpeak frequency value and the reference peak frequency value. Forexample, the calibrated Q_measured_reference value may be obtained byadding the difference between the current peak frequency value and thereference peak frequency value to the Q_measured_reference value.Alternatively, the calibrated Q_measured_reference value may be obtainedby adding a product of the difference between the current peak frequencyvalue and the reference peak frequency value and a predetermined weightto the Q_measured_reference value.

In step 4, the foreign object detection apparatus may compare thequality factor threshold value with the calibrated reference measuredquality factor value to determine whether a foreign object is present.

Upon determining that the foreign object is present, the foreign objectdetection apparatus may stop power transfer and return to the selectionphase 1310. Alternatively, an indicator indicating that the foreignobject is present may be transmitted to the wireless power receiver, andthe wireless power receiver may request End of Power Transfer or ignorethe indicator and proceed to the subsequent phase in order tocontinuously perform charging. In contrast, upon determining that theforeign object is not present, the foreign object detection apparatusmay enter the power transfer phase 1350 to start wireless charging ofthe wireless power receiver.

FIG. 13B is a diagram illustrating a state transition diagram explainingforeign object detection in a foreign object detection apparatusaccording to another embodiment.

Referring to FIG. 13B, when the object is detected in the selectionphase 1311, the foreign object detection apparatus may measure thecurrent quality factor value at the reference operating frequency, thatis, the measured quality factor value Q_measured.

In addition, when the object is detected in the selection phase 1311,the foreign object detection apparatus may measure the quality factorvalues at a plurality of frequencies before entering the ping phase 1321and search for a frequency having a maximum quality factor value, thatis, a current peak frequency F_current_peak.

In the ping phase 1321, the foreign object detection apparatus mayperiodically transmit a predetermined power signal for identifying thewireless power receiver, for example, a digital ping.

The foreign object detection apparatus may store information on themeasured quality factor values and the current peak frequency value inthe predetermined recording region.

When a signal strength indicator is received in the ping phase 1321, theforeign object detection apparatus may enter the identification andconfiguration phase 1331 to identify the wireless power receiver and setvarious configuration parameters for the identified wireless powerreceiver.

When identification and configuration of the wireless power receiverend, the foreign object detection apparatus may enter the negotiationphase 1341 to perform a foreign object detection procedure.

The foreign object detection procedure may be performed through thefollowing four steps.

In step 1, the foreign object detection apparatus may receive at leastone foreign object detection status packet from the identified wirelesspower receiver. Here, the foreign object detection status packet mayinclude at least one of information on the reference peak frequencyvalue and information on the reference quality factor value.

The information on the reference quality factor value may mean a qualityfactor value measured at a reference operating frequency in a state inwhich the wireless power receiver is powered off. Powering off thereceiver may mean a state in which power is not transmitted to a load.The information on the reference peak frequency value may mean afrequency having a maximum quality factor within the operating frequencyband in a state in which only the wireless power receiver is placed inthe charging area of a predetermined wireless power transmitter. Thewireless power receiver may store a reference peak frequency value inadvance and transmit the reference peak frequency value to the wirelesspower transmitter in the negotiation phase 1341.

In step 2, the foreign object detection apparatus may determine aquality factor threshold value for determining whether a foreign objectis present based on the received reference quality factor value.

In step 3, the foreign object detection apparatus may compare thequality factor threshold value with the measured quality factor value todetermine whether a foreign object is present.

Upon determining that the foreign object is present, the foreign objectdetection apparatus according to the embodiment may stop power transferand return to the selection phase 1310. The foreign object detectionapparatus according to another embodiment may transmit a predeterminedforeign object detection indicator indicating that a foreign object ispresent to the wireless power receiver. At this time, when the foreignobject detection indicator is received, the wireless power receiver mayrequest End of Power Transfer or ignore the indicator, that is, may nottransmit an Ack response signal corresponding to the foreign objectdetection indicator, and proceed to the subsequent phase in order tocontinuously perform charging.

In contrast, upon determining that the foreign object is not present,the foreign object detection apparatus may determine whether thereference peak frequency value has been received.

The foreign object detection apparatus according to one embodiment maydetermine that the reference peak frequency value has been received,when the reference peak frequency value included in the foreign objectdetection status packet is greater than 0.

When the reference peak frequency value is not received, the foreignobject detection apparatus may enter the power transfer phase 1350 tostart wireless charging of the wireless power receiver.

When the reference peak frequency value is received, the foreign objectdetection apparatus may determine a peak frequency threshold value basedon the reference peak frequency value.

In step 4, the foreign object detection apparatus may compare the peakfrequency threshold value with the current peak frequency value todetermine whether a foreign object is present. When the current peakfrequency value is greater than the peak frequency threshold value, itis determined that the foreign object is present. Then, the foreignobject detection apparatus may stop power transfer and return to theselection phase 1311. Alternatively, an indicator indicating that theforeign object is present may be transmitted to the wireless powerreceiver, and the wireless power receiver may request End of PowerTransfer or ignore the indicator and proceed to the subsequent phase inorder to continuously perform charging. In contrast, upon determiningthat the foreign object is not present, the foreign object detectionapparatus may enter the power transfer phase 1351 to start wirelesscharging of the wireless power receiver.

As another embodiment, in the embodiment of FIG. 13B, the foreign objectdetection apparatus may first perform a procedure of determining whetherthe reference peak frequency value has been received from the wirelesspower receiver before the foreign object detection procedure based onthe quality factor value.

At this time, upon determining that the reference peak frequency valuehas been received, the foreign object detection apparatus may performthe foreign object detection procedure based on the quality factor valueand the foreign object detection procedure based on the peak frequencyto determine whether a foreign object is present.

In contrast, upon determining that the reference peak frequency valuehas not been received, the foreign object detection apparatus mayperform only the foreign object detection procedure based on the qualityfactor value to determine whether a foreign object is present.

If the foreign object detection procedure is differently performeddepending on whether the reference peak frequency is received, theforeign object detection procedure may be performed in a mannerpreferred by the wireless power receiver. In addition, by previouslysetting the foreign object detection method optimized for a device, inwhich the wireless power receiver is mounted, in the manufacturing step,it is possible to increase foreign object detection accuracy. Of course,it should be noted that a foreign object detection method correspondingto the wireless power receiver, that is, whether reference peakfrequency information is transmitted or not, may be changed throughpredetermined menu settings. In one embodiment, the wireless powerreceiver may identify the type and characteristics of the wireless powertransmitter and determine a foreign object detection method optimizedfor the identified type and characteristics. In this case, the wirelesspower receiver may adaptively determine whether the reference peakfrequency information is transmitted or not according to the determinedforeign object detection method.

FIG. 13C is a diagram illustrating a foreign object detection procedureaccording to another embodiment.

A wireless power transmitter may measure the quality factor value of aresonant circuit when an object is detected in a charging area. Thequality factor of the resonant circuit may mean an amplification ratioof the input/output voltage by the resonant capacitor when AC powerhaving a specific frequency is applied to the resonant circuit. Forthis, refer to the description of FIGS. 11A and 11B. At this time, thequality factor value of each frequency may be measured within theoperating frequency range of the wireless power transmitter.

The wireless power transmitter may determine a current quality factorvalue and a peak frequency (a frequency at which a maximum qualityfactor value is measured in the measured frequency range) throughquality factor measurement and store the current quality factor valueand the peak frequency in a memory.

The wireless power transmitter may receive a foreign object detectionstatus packet. For the foreign object detection status packet, refer tothe description of FIGS. 14A to 14B.

The wireless power transmitter may determine the quality factorthreshold value based on the received reference quality factor value.

The wireless power transmitter may determine whether a foreign object ispresent using the quality factor threshold value and the measuredquality factor value.

For example, when the current quality factor value is greater than orequal to the quality factor threshold value, the wireless powertransmitter may determine that a foreign object is present. When thecurrent quality factor value is less than the quality factor thresholdvalue, the wireless power transmitter may determine whether informationon the reference peak frequency is included in the foreign objectdetection status packet. (see FIG. 14 )

If the information on the reference peak frequency is not included inthe foreign object detection status packet, the wireless powertransmitter may determine that a foreign object is not present. At thistime, a subsequent phase (e.g., calibration or power transfer) forwireless power transfer may be performed.

If the information on the reference peak frequency is included, thewireless power transmitter may further determine whether a foreignobject is present based on the received information on the referencepeak frequency. The wireless power transmitter may determine a peakfrequency threshold value using the reference peak frequency value. Thewireless power transmitter may compare the peak frequency thresholdvalue with the current peak frequency and determine that a foreignobject is present when the current peak frequency is equal to or greaterthan the peak frequency threshold value. In contrast, when the currentpeak frequency is less than the peak frequency threshold value, thewireless power transmitter may determine that a foreign object is notpresent.

Depending on whether a foreign object is present, the wireless powertransmitter may determine whether wireless power transfer is performedor stopped.

In another embodiment, the procedure of determining whether a foreignobject is present based on the quality factor value and the procedure ofdetermining whether a foreign object is present based on the peakfrequency may be performed in a reverse order. That is, the procedure ofdetermining whether a foreign object is present based on the peakfrequency may be performed first and then the procedure of determiningwhether a foreign object is present based on the quality factor value,thereby improving foreign object detection capability.

FIG. 13D is a diagram illustrating a foreign object detection procedureaccording to another embodiment.

Referring to FIG. 13D, a wireless power transmitter may measure thequality factor value of a resonant circuit when an object is detected ina charging area. The quality factor of the resonant circuit may mean anamplification ratio of the input/output voltage by the resonantcapacitor when AC power having a specific frequency is applied to theresonant circuit. For this, refer to the description of FIGS. 11A and11B. At this time, the quality factor value of each frequency may bemeasured within the operating frequency range of the wireless powertransmitter.

The wireless power transmitter may store the measured quality factorvalue of each frequency in a predetermined memory.

The wireless power transmitter may receive a foreign object detectionstatus packet.

Here, the foreign object detection status packet may include informationon a reference peak frequency corresponding to a frequency, at which amaximum quality factor value is measured within an operating frequency,and information on a reference quality factor value corresponding to themaximum quality factor value.

The wireless power transmitter may determine the quality factorthreshold value based on the reference quality factor value.

The wireless power transmitter may determine whether a foreign object ispresent using the quality factor threshold value and the measuredquality factor value. At this time, the measured quality factor valuemay be a quality factor value measured at a frequency corresponding tothe received reference peak frequency. Since the measured quality factorvalue of each frequency is stored in the memory, the wireless powertransmitter may identify a frequency corresponding to the receivedreference peak frequency and read the measured quality factor value fromthe memory in correspondence with the identified frequency.

The frequency at which the quality factor value is changed most greatlydepending on presence/absence of the foreign object is a reference peakfrequency. Accordingly, the wireless power receiver may transmit thereference peak frequency and the quality factor value measured at thereference peak frequency to the wireless power transmitter, and thewireless power transmitter may determine whether a foreign object ispresent based on the received information. At this time, when thereference quality factor value corresponding to the reference peakfrequency at which the quality factor value is changed most greatlydepending on presence/absence of the foreign object is compared with thecurrent quality factor value, it is possible to improve foreign objectdetection capability. Here, the current quality factor valuecorresponding to the reference peak frequency may be measured before theping phase, without being limited thereto.

In another embodiment, the wireless power transmitter may determinewhether a foreign object is present only using information on thereference peak frequency included in the foreign object detection statuspacket.

If the frequency corresponding to the maximum quality factor value amongthe quality factor values measured before the ping phase is greater thanthe reference peak frequency (which may be determined in considerationof a certain tolerance range), it may be determined that the foreignobject is present.

FIG. 14A is a view illustrating the structure of an FOD status packetmessage according to an embodiment.

Referring to FIG. 14A, the FOD status packet message 1400 may have alength of 2 bytes, and include a first data 1401 field having a lengthof 6 bits, a mode 1402 field having a length of 2 bits and a referencequality factor value 1403 field having a length of 1 byte.

As denoted by reference numeral 1404, if the mode 1402 field is set to abinary value of “00”, all bits of the first data 1401 field are recordedas 0 and information corresponding to the reference quality factor valuemeasured and determined in a state in which the wireless power receiveris powered off is recorded in the reference quality factor value 1403field. In contrast, if the mode 1402 field is set to a binary value of“01”, information corresponding to the reference peak frequency valuemeaning a frequency having a maximum quality factor value within theoperating frequency band in a state in which only the wireless powerreceiver is placed in the charging area may be recorded in the firstdata 1401 field. At this time, information corresponding to thereference quality factor value measured and determined in a state inwhich the wireless power receiver is powered on may be recorded in thereference quality factor value field 1403. The resolution of thereference peak frequency value recorded in the first data 1401 may bedetermined based on the size of the operating frequency band.

As shown in FIG. 14A, the first data 1401 may have a value from 0 to 63.In the case where the operating frequency band is 100 kHz to 260 kHz,when the first data 1401 is 0, this may mean that the reference peakfrequency is 100 kHz, and, when the first data 1401 is 63, this may meanthat the reference peak frequency is 260 kHz. At this time, theresolution of the reference peak frequency value may be set to 160kHz/64=2.5 kHz obtained by dividing the operating frequency bandwidth bythe number of first data 1410.

Alternatively, the operating frequency band for quality factormeasurement may be 87 kHz to 150 kHz. At this time, any frequency valuefrom 87 kHz to 150 kHz may be indicated in the first data 1401.

FIG. 14B is a view illustrating the structure of an FOD status packetmessage according to another embodiment.

Referring to FIG. 14B, the FOD status packet message 1410 may have alength of 2 bytes, and include a first data 1411 field having a lengthof 6 bits, a mode 1412 field having a length of 2 bits and a referencequality factor value 1413 field having a length of 1 byte.

As denoted by reference numeral 1414, if the mode 1412 field is set to abinary value of “00”, information corresponding to a reference peakfrequency value meaning a frequency having a maximum quality factorvalue within an operating frequency band in a state in which only thewireless power receiver is placed in the charging area may be recordedin the first data 1401 field. If the first data 1411 is 0, the foreignobject detection apparatus may determine that the wireless powerreceiver does not transmit the reference peak frequency value. At thistime, information corresponding to the reference quality factor valuemeasured and determined in a state in which the wireless power receiveris powered off may be recorded in the reference quality factor valuefield 1413. The resolution of the reference peak frequency valuerecorded in the first data 1401 may be determined based on the size ofthe operating frequency band.

As shown in FIG. 14B, the first data 1411 may have a value from 1 to 63.In the case where the operating frequency band is 100 kHz to 260 kHz,when the first data 1411 is 1, this may mean that the reference peakfrequency is 100 kHz, and, when the first data 1411 is 63, this may meanthat the reference peak frequency is 260 kHz. At this time, theresolution of the reference peak frequency value may be determined to160 kHz/63=2.54 kHz obtained by dividing the operating frequencybandwidth by the number of first data 1411.

Alternatively, the operating frequency band for quality factormeasurement may be 87 kHz to 149 kHz. At this time, any frequency valuefrom 87 kHz to 149 kHz may be indicated in the first data 1411.

In another embodiment, the foreign object detection status packets ofFIGS. 14A and 14B may include information on the reference peakfrequency corresponding to the frequency at which the maximum qualityfactor value is measured within the operating frequency and informationon the reference quality factor value which is the quality factor valuecorresponding to the maximum quality factor value. The information onthe reference peak frequency and the reference quality factor value maybe stored in the memory of the wireless power receiver. This may bemeasured in advance using a specific wireless power transmitter in amanufacturing process. Here, the specific wireless power transmitter isa standard transmitter and is used for authentication. In actualproducts, the measured value of the standard transmitter may becalibrated and used in consideration of differences in design andcharacteristics between the actual products and the standardtransmitter.

When the FOD status packet of FIG. 14 is received, the wireless powertransmitter may compare the reference quality factor value with thequality factor value measured in the ping phase 520 (or before the pingphase) to determine whether a foreign object is present (Method 1) orcompare the reference peak frequency with the peak frequency measured inthe ping phase 520 (or before the ping phase) to determine whether aforeign object is present (Method 2, the embodiments of FIG. 11 ).

Alternatively, whether a foreign object is present may be determinedusing a complex method.

In one embodiment, the wireless power transmitter may determine whethera foreign object is present using Method 1. At this time, two thresholdvalues (threshold value 1: Q_Threshold 1 and threshold value 2:Q_Threshold 2) may be determined based on the received reference qualityfactor value. Here, the threshold value 1 is greater than the thresholdvalue 2.

When the measured quality factor value measured before the ping phase520 is less than the threshold value 2, the wireless power transmittermay determine that a foreign object is present.

When the measured quality factor value measured before the ping phase520 is less than the threshold value 1 and equal to or greater than thethreshold value 2, the wireless power transmitter may determine whethera foreign object is present using Method 2.

FIG. 15 is a view illustrating the structure of an FOD status packetmessage according to another embodiment.

Referring to FIG. 15 , the FOD status packet message 1500 may have alength of 2 bytes, and include a reserved 1501 field having a length of6 bits, a mode 1502 field having a length of 2 bits and a referencevalue 1503 field having a length of 1 byte. Here, all bits of thereserved 1501 field are recorded as “0”.

As denoted by reference numeral 1504, if the mode 1502 field is set to“00”, information corresponding to a reference quality factor valuemeasured and determined in a state in which the wireless power receiveris powered off may be recorded in the reference value 1503 field.

In contrast, if the mode 1502 field is set to a binary value of “01”,information corresponding to a reference peak frequency value meaning afrequency having a maximum quality factor value within an operatingfrequency band in a state in which only the wireless power receiver isplaced in the charging area may be recorded in the reference value 1503field. At this time, the reference peak frequency may be searched in astate in which a foreign object is not placed but only the wirelesspower receiver which is powered off is present in the charging area.

In the present embodiment, the foreign object detection apparatus (orthe wireless power transmission apparatus) may receive a plurality ofFOD status packets in the negotiation phase to acquire the referencepeak frequency value and the reference quality factor valuecorresponding to the wireless power receiver.

For example, if the value recorded in the reference value 1503 is areference peak frequency, the resolution of the reference peak frequencyvalue may be determined based on the size of the operating frequencyband, that is, the operating frequency bandwidth.

If the operating frequency bandwidth of the wireless charging system is256 kHz, the resolution of the reference peak frequency value may be 256kHz/128=2 kHz.

As shown in FIG. 15 , since the reference value 1503 field has a lengthof 1 byte, the reference value 1503 may have a value from 0 to 127. Forexample, when the wireless power transmission apparatus having anoperating frequency band of 100 kHz to 356 kHz receives an FOD statuspacket in which the mode 1502 value is a binary value of “01” and thereference value 1503 is set to “0x05”, the wireless power transmissionapparatus may recognize that the reference peak frequency correspondingto the wireless power receiver is 100 kHz+5*2 kHz=110 kHz.

FIG. 16 is a flowchart illustrating a foreign object detection method ina wireless power transmission apparatus according to an embodiment.

Referring to FIG. 16 , when an object placed in the charging area isdetected in the selection phase, the wireless power transmissionapparatus may measure and store a quality factor value corresponding toa reference operating frequency in a predetermined recording regionbefore entering the ping phase (S1601 to S1602). At this time, thevoltage of the transmission coil is 0.5 Vrms to 2 Vrms. It is possibleto prevent current leakage of the rectifier of the wireless powerreceiver. Here, rms means root mean square.

In addition, the wireless power transmission apparatus may search forand store a current peak frequency having a maximum quality factor valueamong quality factor values measured at a plurality of frequencies inthe operating frequency band in a predetermined recording region(S1603). Here, it should be noted that a frequency offset (or the numberof frequencies) for determining frequencies at which the quality factorvalue is measured for searching for the current peak frequency withinthe operating frequency band may vary according to the design of thoseskilled in the art (S1603).

In the present embodiment, the operating frequency band may be 87 kHz to150 kHz and the reference operating frequency may be 100 kHz, withoutbeing limited thereto.

When searching of the current peak frequency ends, the wireless powertransmission apparatus may enter the ping phase to wirelessly transmit adigital ping signal for identifying the wireless power receiver.

When a signal strength indicator is received in response to the digitalping signal, the wireless power transmission apparatus may enter theidentification and configuration phase and transition to the negotiationphase when identification and configuration of the wireless powerreceiver end (S1604).

The wireless power transmission apparatus may determine a thresholdvalue (or a threshold range) for determining whether a foreign object ispresent based on the received FOD status packet (S1605). Here, thethreshold value may be a quality factor threshold value determined basedon the reference quality factor value included in the FOD status packet,without being limited thereto.

The wireless power transmission apparatus may calibrate (or compensatefor) the measured quality factor value, that is, the reference measuredquality factor value, in correspondence with the reference operatingfrequency based on a difference between the reference peak frequencyvalue included in the FOD status packet received in the negotiationphase and the current peak frequency value (S1606).

The wireless power transmission apparatus may compare the calibratedreference measured quality factor value with the determined qualityfactor threshold value to determine whether a foreign object is present(S1607).

Upon determining that the foreign object is present, the wireless powertransmission apparatus may perform control to stop power signal transferand to output a predetermined warning alarm indicating that the foreignobject has been detected (S1608 and S1609).

Upon determining that the foreign object is not present in step 1608,the wireless power transmission apparatus may enter the power transferphase and start charging of the wireless power receiver (S1608 andS1610). At this time, a calibration procedure for optimizing variousconfiguration parameters necessary for power transfer and power controlmay be further performed before charging of the wireless power receiverstarts.

FIG. 17 is an experimental result table illustrating a reference peakfrequency of each receiver type and change in peak frequency accordingto placement of a foreign object.

Referring to FIG. 17 , the reference peak frequency 1710 acquired in astate in which only the wireless power receiver is placed in thecharging area and the quality factor value 1720 measured at thereference peak frequency differ according to the receiver type.

In particular, referring to reference numerals 1710 and 1730, it can beseen that the peak frequency 1730 when the wireless power receiver andthe foreign object are placed in the charging area is greater than thepeak frequency 170 when only the wireless power receiver is placed.

In addition, referring to reference numerals 1720 and 1740, it can beseen that the quality factor value measured when the wireless powerreceiver and the foreign object are placed in the charging area is lessthan the quality factor value measured when only the wireless powerreceiver is placed.

In addition, referring to reference numeral 1750, it can be seen thatthe peak frequency decreases but the quality factor value increases asthe position of the foreign object placed in the charging area movesaway from the center.

FIG. 18 is an experimental result graph showing change in quality factorvalue and peak frequency according to placement of a foreign object in awireless charging system according to an embodiment.

Referring to FIG. 18 , when a first receiver and a foreign object areplaced in the charging area, the peak frequency is greater than that ofthe case where only the first receiver is placed in the charging area byΔf. Hereinafter, for convenience of description, Δf is referred to as apeak frequency shift value. In contrast, it can be seen that the qualityfactor value measured at the peak frequency corresponding to the statein which the first receiver and the foreign object are placed in thecharging area, that is, the current peak frequency, is less than thequality factor value measured at the peak frequency corresponding to thestate in which only the first receiver is placed, that is, the referencepeak frequency, by ΔQ. Hereinafter, for convenience of description, ΔQis referred to as a quality factor shift value.

As shown in FIG. 18 , results similar to the experimental result of thefirst receiver are obtained with respect to the remaining second tofourth receivers.

The foreign object detection apparatus according to an embodiment maycalibrate the reference measured quality factor value based on the peakfrequency shift value and the quality factor shift value. For example,as the sum of the peak frequency shift value and the quality factorshift value increases, the calibration ratio of the reference qualityfactor value may increase.

For example, the foreign object detection apparatus may receive thequality factor value (hereinafter referred to as a first maximum qualityfactor value, for convenience of description) corresponding to thereference peak frequency from the wireless power receiver in thenegotiation phase. When the object is detected in the selection phase,the foreign object detection apparatus may measure the quality factorvalue at a plurality of frequencies within the operating frequency bandto search for the current peak frequency. At this time, the qualityfactor value corresponding to the searched current peak frequency isreferred to as a second maximum quality factor value. The foreign objectdetection apparatus may determine a value obtained by subtracting thesecond maximum quality factor value from the first maximum qualityfactor value as a quality factor shift value. In the foreign objectdetection status packets of FIGS. 14 to 15 , a predetermined data fieldfor additionally recording the first maximum quality factor value may bedefined.

In general, in the case of a wireless charging system, a resonantphenomenon occurs at a peak frequency having a maximum quality factorvalue and power efficiency is maximized when the resonant phenomenonoccurs.

FIG. 19 is a block diagram illustrating the configuration of a foreignobject detection apparatus according to another embodiment.

Referring to FIG. 19 , the foreign object detection apparatus 1900 mayinclude a peak frequency search unit 1910, an output voltage measurementunit 1920, a quality factor slope determination unit 1930, a foreignobject detection unit 1940 and a controller 1950. The components of theforeign object detection apparatus 1900 are not necessarily mandatoryand some components may be added or deleted.

Upon detecting that the object is placed in the charging area in theselection phase, the peak frequency search unit 1910 may temporarilystop power transfer and search for a frequency having a maximum qualityfactor value within the operating frequency band. Here, a frequencysearch offset for searching for the frequency having the maximum qualityfactor value is determined in units of 10 kHz*k (k being a naturalnumber). However, the embodiment is not limited thereto and thefrequency search offset may be defined in fewer or greater units.Hereinafter, for convenience of description, the frequency having themaximum quality factor value within the operating frequency bandsearched after the object is detected is referred to as a current peakfrequency F_current_peak. In contrast, a frequency having a maximumquality factor value acquired through the preliminary experiment in astate in which only the wireless power receiver is placed in thecharging area is referred to as a reference peak frequencyF_reference_peak.

The output voltage measurement unit 1920 may measure the output voltagelevel at a specific frequency within the operating frequency band. Forexample, the frequency at which the output voltage level is measured mayinclude at least one of the start frequency F_start of the operatingfrequency band, the searched current peak frequency, and the endfrequency F_end of the operating frequency band. The output voltagelevel may be the strength of the voltage applied to the transmissioncoil of the resonant circuit. However, the embodiment is not limitedthereto and the measurement position of the output voltage level mayvary according to the design of those skilled in the art.

The quality factor slope determination unit 1930 may calculate a qualityfactor slope based on the voltage value of a specific frequency measuredby the output voltage measurement unit 1920. For example, the outputvoltage level measured at the start frequency and the output voltagelevel measured at the current peak frequency are referred to as V_start′and Vc′, respectively. At this time, the quality factor slope Q_slope′may be calculated by the following equation:

(Vc′−V_start′)/(F_current_peak−F_start)

as denoted by reference numeral 2020 of FIG. 20 .

Although the quality factor slope is calculated based on the measurementvoltage level in the embodiments of FIGS. 19 to 21 , this is merely anembodiment. In another embodiment, the quality factor slope may becalculated based on the quality factor value measured at thecorresponding frequency.

The quality factor slope Q_slope′ may be calculated based on the outputvoltage level Vc′ measured at the current peak frequency and the outputvoltage level V_end′ measured at the end frequency according to anotherembodiment. In this case, the quality factor slope may be calculated bythe following equation:

(Vc′−V_end′)/(F_current_peak−F_end)

Hereinafter, for convenience of description, the quality factor slopecalculated based on the output voltage levels (or the quality factorvalues) measured at the start frequency and the current peak frequencyis referred to as a first quality factor slope and a quality factorslope calculated based on the output voltage levels (or the qualityfactor values) measured at the current peak frequency and the endfrequency is referred to as a second quality factor slope.

The foreign object detection unit 1940 may compare the calculatedquality factor slope with a predefined threshold value to detect aforeign object placed in the charging area.

For example, the foreign object detection unit 1940 may compare thecalculated first quality factor slope with a predefined first qualityfactor slope threshold value to determine whether a foreign object ispresent. Here, the first quality factor slope threshold value may have apositive value.

In another example, the foreign object detection unit 1940 may comparethe calculated second quality factor slope with a predefined secondquality factor slope threshold value to determine whether a foreignobject is present. Here, the second quality factor slope threshold valuemay have a positive value.

The first quality factor slope threshold value may be included in theforeign object detection status packet of FIG. 15 and may be receivedfrom the wireless power receiver. At this time, the first quality factorslope threshold value may be recorded in the reference value field.However, this is merely one embodiment and a new field for recording thefirst quality factor slope threshold value may be defined in the foreignobject detection status packet.

In another example, the foreign object detection unit 1940 may calculatean average value of the first quality factor slope and the secondquality factor slope and compare the calculated quality factor slopeaverage value with a predefined quality factor slope threshold value,thereby determining whether a foreign object is present. Here, theaverage value may be calculated by dividing a difference between thesecond quality factor slope and the first quality factor slope by 2.

As shown in FIG. 20 , the absolute value of the quality factor slopecalculated when only the receiver is placed in the charging area isgreater than that of the quality factor slope calculated when thereceiver and the foreign object are placed.

Accordingly, the foreign object detection unit 1940 may determine thatthe foreign object is placed in the charging area, when the calculatedfirst quality factor slope is less than the first quality factor slopethreshold value.

The foreign object detection unit 1940 may determine that the foreignobject is not present in the charging area, when the calculated firstquality factor slope is equal to or greater than the first qualityfactor slope threshold value.

For example, the first quality factor slope threshold value may bepredefined based on the type of the wireless power receiver andmaintained in a predetermined recording region of the foreign objectdetection apparatus 1950.

In another example, the first quality factor slope threshold value maybe the same in all wireless power receivers.

In another example, the first quality factor slope threshold value maybe directly received from the wireless power receiver through acommunication unit (not shown). At this time, the foreign objectdetection apparatus 1900 may acquire the first quality factor slopethreshold value and/or the second quality factor slope threshold valuethrough the foreign object detection (FOD) status packet received in thewireless power receiver in the negotiation phase.

The controller 1950 may control overall operation of the foreign objectdetection apparatus 1900, and temporarily stop power transfer to thewireless power receiver and control an alarm unit (not shown) configuredto output a predetermined warning alarm indicating that the foreignobject is present in the charging area, when the foreign object isdetected by the foreign object detection unit 1940.

In addition, the controller 1950 may monitor whether the detectedforeign object has been removed after outputting the warning alarm. Ifthe foreign object has been removed as the monitoring result, thecontroller 1950 may perform control to release the warning alarm and toresume power transfer to the wireless power receiver.

FIG. 20 is a view illustrating change in quality factor slope dependingon whether a foreign object is present in a wireless charging systemaccording to an embodiment.

Referring to FIG. 20 , reference numeral 2010 shows an example in whichthe quality factor slope is calculated in a state in which only thewireless power receiver is placed in the charging area and referencenumeral 2020 shows an example in which the quality factor slope iscalculated in a state in which the wireless power receiver and theforeign object are placed in the charging area. It can be seen from FIG.20 that the quality factor slope Q_slope′ calculated in the state inwhich the foreign object is further placed in the charging area is lessthan the quality factor slope Q_slope calculated in the state in whichonly the wireless power receiver is placed in the charging area.

Hereinafter, for convenience of description, Q_slope and Q_slope′ arereferred to as a reference quality factor slope and a current qualityfactor slope, respectively.

The quality factor slope threshold value according to an embodiment maybe set to any value less than the reference quality factor slope ofreference numeral 2010 and greater than the current quality factor slopeof reference numeral 2020.

FIG. 21A is a flowchart illustrating a foreign object detection methodin a wireless power transmission apparatus according to anotherembodiment.

Referring to FIG. 21A, the wireless power transmission apparatus maydetect an object placed in the charging area in the selection phase(S2101).

When the object is detected, the wireless power transmission apparatusmay temporarily stop power transfer before entering the ping phase,search for a current peak frequency having a maximum value among thequality factor values measured at a plurality of frequencies within theoperating frequency band, and store the current peak frequency in apredetermined recording region (S2102).

Here, it should be noted that a frequency offset (or the number offrequencies) for determining frequencies at which the quality factorvalue is measured in order to search for the current peak frequencywithin the operating frequency band may vary according to the design ofthose skilled in the art. In addition, the operating frequency band mayvary according to the design of the wireless charging system and theapplied standard.

The wireless power transmission apparatus may measure the output voltagelevels respectively corresponding to the start frequency and the endfrequency of the operating frequency band (S2103).

The wireless power transmission apparatus may calculate the qualityfactor slope based on the output voltage levels measured at the startfrequency and the current peak frequency (S2004). Here, the qualityfactor slope Q_slope′ may be calculated by dividing a difference betweenthe output voltage level Vc′ measured at the current peak frequencyF_current_peak and the output voltage level V_start′ measured at thestart frequency F_start by a difference between the current peakfrequency and the start frequency. That is, the quality factor slope maybe calculated by the following equation:

Q_slope′=(Vc′−V_start′)/(F_current_peak−F_start)

The wireless power transmission apparatus may compare the calculatedquality factor slope with a predetermined quality factor slope thresholdvalue to determine whether a foreign object is present (S2105).

Upon determining that the foreign object is present, the wireless powertransmission apparatus may perform control to stop power signal transferand to output a predetermined warning alarm indicating that the foreignobject has been detected (S2106 and S2107).

Upon determining that the foreign object is not present in step 2105,the wireless power transmission apparatus may enter the power transferphase and start charging of the wireless power receiver (S2106 andS2108).

FIG. 21B is a flowchart illustrating a foreign object detection methodin a wireless power transmission apparatus according to anotherembodiment.

Referring to FIG. 21B, the wireless power transmission apparatus maydetect an object placed in the charging area in the selection phase(S2111).

When the object is detected, the wireless power transmission apparatusapplies a low voltage (e.g., 0.5 to 2V) to the inverter 1120 beforeentering the ping phase to measure the quality factor value at aplurality of frequencies within the operating frequency band.

The controller 1180 may store the quality factor value measured at aspecific frequency in a predetermined recording region (S2112). Forexample, the specific frequency may be a predefined frequency within theoperating frequency band, and may be used interchangeably with ameasurement start frequency for convenience of description. In addition,the quality factor value measured at the measurement start frequency isreferred to as a start quality factor value.

The controller 1180 may determine a current peak frequency, at which amaximum value is measured, among the measured quality factor values andstore the current peak frequency and the peak quality factor valuemeasured at the corresponding frequency in a predetermined recordingregion (S2113).

Here, it should be noted that a frequency offset (or the number offrequencies) for determining frequencies at which the quality factorvalue is measured in order to search for the current peak frequencywithin the operating frequency band may vary according to the design ofthose skilled in the art. In addition, the operating frequency band mayvary according to the design of the wireless charging system and theapplied standard.

The wireless power transmission apparatus may calculate the qualityfactor slope based on the quality factor values measured at a specificfrequency (start frequency) and the current peak frequency (S2114). Thequality factor slope Q_slope′ may be determined as follows.

Q_slope′=(Qc′−Q start′)/(F_current_peak−F_start)

where, F_current_peak denotes a current peak frequency, F_start denotesa specific frequency (start frequency), Qc′ denotes a peak qualityfactor value, and Q_start′ denotes a start quality factor value.

The wireless power transmission apparatus may compare the calculatedquality factor slope with a predetermined quality factor slope thresholdvalue to determine whether a foreign object is present in the chargingarea (S2115).

In another embodiment, the predetermined quality factor slope thresholdvalue may be determined based on the information included in the foreignobject detection status packet as in the embodiment of FIG. 14 .

For example, in the foreign object detection status packet, a field fortransmitting information on the quality factor slope threshold value ora value of an angle unit corresponding to the quality factor slopethreshold value may be defined.

Upon determining that the foreign object is present, the wireless powertransmission apparatus may perform control to temporarily stop powertransfer and to output a predetermined warning alarm indicating that theforeign object has been detected (S2116 and S2117).

Upon determining that the foreign object is not present in step 2115,the wireless power transmission apparatus may enter the power transferphase and start charging of the wireless power receiver (S2116 andS2118).

Although the quality factor slope is calculated based on the outputvoltage levels measured at the start frequency and the current peakfrequency in the embodiments of FIGS. 19 to 21A and 21B, this is merelyan embodiment. In another embodiment, the quality factor slope may becalculated based on the quality factor values measured at the startfrequency and the current peak frequency. It should be noted that,instead of the output voltage measurement unit 1920 shown in FIG. 19 , aquality factor measurement unit (not shown) for measuring the qualityfactor values corresponding to the start frequency and the current peakfrequency is included in the foreign object detection apparatus 1900.

The method according to the foregoing embodiments may be implemented ascode that can be written to a computer-readable recording medium and canthus be read by a computer. Examples of the computer-readable recordingmedium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk,an optical data storage, and a carrier wave (e.g., data transmissionover the Internet).

The computer-readable recording medium can be distributed over aplurality of computer systems connected to a network so thatcomputer-readable code is written thereto and executed therefrom in adecentralized manner. Functional programs, code, and code segmentsneeded to realize the embodiments herein can be construed by one ofordinary skill in the art.

Those skilled in the art will appreciate that the disclosure may becarried out in other specific ways than those set forth herein withoutdeparting from the spirit and essential characteristics of thedisclosure.

The above exemplary embodiments are therefore to be construed in allaspects as illustrative and not restrictive. The scope of the disclosureshould be determined by the appended claims and their legal equivalents,not by the above description, and all changes coming within the meaningand equivalency range of the appended claims are intended to be embracedtherein.

The foreign object detection method according to the embodiment may beused in a wireless charging system for detecting a foreign objectlocated between a wireless power transmitter and a wireless powertransmitter using a quality factor value.

What is claimed is:
 1. A power transmission method for a wireless powertransmitter, the power transmission method comprising: receiving, from awireless power receiver, a packet including a foreign object detection(FOD) status packet; determining whether a foreign object is present ina charging area of the wireless power transmitter based on the FODstatus packet; and generating a foreign object detection indicatorindicating whether the foreign object is present in the charging area ofthe wireless power transmitter based on a result of the determinationand transmitting the generated foreign object detection indicator to thewireless power receiver, wherein the FOD status packet includesinformation on a reference quality factor or a reference peak frequency,and wherein the packet further includes at least one of a signalstrength packet, an end power transfer packet, a power control hold-offpacket, a configuration packet, an identification packet fortransmitting receiver identification information, an extensionidentification packet, a general request packet, a special requestpacket, a control error packet, a renegotiation packet, a 24-bitreception power packet, an eight-bit reception power packet, and acharging status packet.
 2. The power transmission method of claim 1,wherein the FOD status packet includes a mode field, and wherein the FODstatus packet includes information corresponding to one of the referencequality factor and the reference peak frequency based on the mode field.3. The power transmission method of claim 1, further comprising:transmitting sequentially a plurality of sensing signals to the wirelesspower receiver through transmission coils to sense a presence of thewireless power receiver; identifying transmission coils that receives asignal strength indictor transmitted from the wireless power receiver inresponse to the plurality of sensing signals; and selecting, as a powertransmission coil, a transmission coil that receives a signal strengthindicator having the largest amount or the largest value among thetransmission coils.
 4. The power transmission method of claim 1, whereinthe FOD status packet has a length of two bytes, wherein one byte of theFOD status packet includes a six-bit reservation field and a two-bitmode field, and wherein all bits of the reservation field are recordedas zero.
 5. The power transmission method of claim 1, furthercomprising: receiving, from the wireless power receiver, at least one ofa signal strength packet, an end power transfer packet, a power controlhold-off packet, a control error packet, a renegotiation packet, aneight-bit reception power packet, and a charging status packet to whicha byte encoding technique is applied, wherein the byte encodingtechnique is a technique of inserting a start bit, a stop bit, and aparity bit into an encoded binary bit stream of a packet having a lengthof 8 bits.
 6. The power transmission method of claim 1, furthercomprising: a power transmission operation of performing a first powertransmission procedure when the foreign object detection indicatorincludes an ACK response signal, or performing a second powertransmission procedure that requests termination of power transmissionor performing a third power transmission procedure that is differentfrom the termination of the power transmission when the foreign objectdetection indicator includes a NAK response signal.
 7. The powertransmission method of claim 1, wherein the FOD status packet includes afirst FOD status packet including information on the reference qualityfactor and a second FOD status packet including information on thereference peak frequency.
 8. The power transmission method of claim 7,wherein a mode field value of the first FOD status packet is “00”, and amode field value of the second FOD status packet is “01”.
 9. The powertransmission method of claim 7, wherein the foreign object detectionindicator includes a first foreign object detection indicator indicatingwhether the foreign object is present in the charging area of thewireless power transmitter in response to the first FOD status packetand a second foreign object detection indicator indicating whether theforeign object is present in the charging area of the wireless powertransmitter in response to the second FOD status packet.
 10. The powertransmission method of claim 9, further comprising: performing orterminating charging based on the first foreign object detectionindicator and the second foreign object detection indicator.